How To Remember What You Learn

Around 2,500 years ago, the Greek poet Simonides of Ceos was hired to perform at a banquet given by a wealthy man named Scopas. The story comes down to us from the Roman statesman Cicero, who told it in his book On the Orator.

According to Cicero, Simonides recited a poem in honor of his host, but he included a passage praising the twin Gods Castor and Pollux. Scopas was annoyed and told Simonides he would pay him only half the agreed fee, and that he could collect the other half from the Gods.

A little later, a message came in that two young men were waiting outside to see Simonides. He got up and went out, but he found no one there. While he was outside, the roof of the banquet hall collapsed, killing Scopas and everyone else inside. The bodies were so badly crushed that their families couldn't tell who was who.

Simonides remembered where each guest had been sitting at the table, and by picturing the room, he was able to name every person by their place. Cicero says this experience showed Simonides that the best aid to a clear memory is orderly arrangement: if you attach what you want to remember to places in a picture you can walk through in your mind, you can recall it in order.

That idea became the method of loci, also called the memory palace, and it was taught to students of public speaking in Greece and Rome for centuries.

Whether every detail of the story is true, nobody can say. But the method it describes is real, and modern research shows it works. More importantly, the story points at something many people never learn: memory can be built, organized, and trained.

Most of us experience memory as something that happens to us. You read a book you loved, and three months later you can remember the title and one idea. You sit through a training at work and can't recall most of it by the following week. You study hard for an exam, pass it, and lose almost all of it by the next semester. You meet someone, hear their name, and lose it before the conversation is over. You may have decided you just have a bad memory.

For anyone trying to become exceptional at anything, that's a serious problem. Every skill, every field, and every career is built on what you know and can use. If most of what you learn leaks out within weeks, you're putting in a lot of time and keeping very little of it.

This article covers how memory actually works, why you forget, why most people's study habits barely work, what does work and why, how meaning, curiosity, emotion, and context shape what sticks, the techniques memory champions use, how your body and your age affect your memory, and how to decide what's worth remembering at all.

It ends with a complete system you can use for anything you want to learn. Along the way, we'll follow Theo, a 34-year-old who reads around 20 books a year, is studying for a professional certification, and has noticed that he can barely remember any of it.

Remembering anything takes three steps. First, the information has to get in, which psychologists call encoding. Then it has to be kept, which is storage. And finally, you have to be able to get it back out when you need it, which is retrieval.

A memory can fail at any of the three. If you weren't really paying attention, it may never have been encoded. If it was encoded but not kept, it faded from storage. And sometimes it's stored but you can't retrieve it, like a name on the tip of your tongue that comes back an hour later.

Psychologists distinguish between a few main kinds of memory. In 1972, the psychologist Endel Tulving drew a line between episodic memory, your memory of things that happened to you, like your first day at a job, and semantic memory, your memory of facts and knowledge, like the capital of France or what a word means. Both are things you can consciously recall and put into words.

The third kind is procedural memory: knowing how to do something, like riding a bike, typing, or playing a song on the piano. It works so differently that it can keep working even when the ability to form other kinds of memories is lost.

In the 1950s, a man known in research as H.M. had parts of his brain removed to stop severe seizures. Afterward, he could no longer form new memories of facts or events. But when the psychologist Brenda Milner had him practice tracing a star while looking only at its reflection in a mirror, he got better day after day, even though each day he had no memory of ever having done the task before.

This article is mostly about the first two kinds, remembering knowledge and experiences, because that's what people mean when they say they forget what they learn. Building skills is covered in more depth in our article "How to Master Anything."

Before anything reaches long-term memory, it passes through what psychologists call working memory: the small mental space where you hold and work with information in the moment, like keeping a phone number in your head while you dial it.

Working memory is tiny. Reviewing decades of research, the psychologist Nelson Cowan concluded in 2001 that people can hold only about three to five meaningful chunks of information in it at once. That's why a long lecture or a dense chapter can feel like it's washing over you. You can only take in a little at a time, and if it isn't processed into long-term memory, it's gone.

What decides whether something makes it into long-term memory? One of the biggest factors is how deeply you think about it.

In a classic set of experiments published in 1975, Fergus Craik and Endel Tulving showed people a series of words and asked different questions about each one.

Some questions were shallow, like whether the word was printed in capital letters. Some were about sound, like whether it rhymed with another word. And some were about meaning, like whether it would fit in a particular sentence.

Later, people remembered the words they had thought about in terms of meaning far better than the words they had only judged by their appearance. The more you think about what something means, the more likely you are to keep it.

Theo realized this described his reading. He read fast, mostly on his phone in short bursts between other things, and he rarely stopped to think about what a chapter actually meant for his work. Much of what he read was never deeply encoded at all.

In the 1880s, the German psychologist Hermann Ebbinghaus became the first person to measure forgetting scientifically, by memorizing lists of nonsense syllables and testing himself at different delays. Our article "How to Master Anything" covers his famous forgetting curve.

In 2015, the psychologists Jaap Murre and Joeri Dros repeated his experiment as closely as they could, with one of them spending about 70 hours learning and relearning lists in the same way. Their results closely matched what Ebbinghaus had found more than a century earlier: forgetting is fastest right after learning, then slows down over time.

The psychologists Robert and Elizabeth Bjork have offered one of the most useful ways to think about forgetting. They argue that every memory has two different strengths. Storage strength is how well the memory is built into your mind and connected to other things you know. Retrieval strength is how easily you can bring it to mind right now.

The two don't always match. Something you just read has high retrieval strength, since it's right there, but it may have very low storage strength, which means it may be gone in a week. And something you learned well years ago, like the phone number of a childhood home, may be hard to retrieve today but come back quickly with a small reminder, because its storage strength is still high.

When you reread a chapter and it feels clear, you're feeling high retrieval strength. It feels like learning, but it doesn't mean the memory is well stored. And according to the Bjorks, the moments when retrieval is hard, when you have to work to bring something back, are the ones that do the most to build storage strength. That idea comes up again and again in the rest of this article.

It's natural to wish you could forget nothing. But the case of a Russian man named Solomon Shereshevsky shows why forgetting is useful. In the 1920s, he worked as a newspaper reporter in Moscow, and his editor noticed he never took notes but could repeat everything he'd been told.

He was sent to the psychologist Alexander Luria, who studied him for about 30 years. Luria found that Shereshevsky could memorize long lists of numbers, words, or nonsense formulas, and recall them perfectly, even years later.

But his memory came with real problems. Every word he heard set off vivid images, sounds, and even tastes, and those images crowded into his mind and got in the way. He had trouble understanding abstract ideas and figurative language, because he couldn't get past the literal pictures each word produced.

He struggled to recognize faces, because people's faces kept changing with their expressions, and he remembered each version. And he struggled to forget things he no longer needed, to the point that he tried writing them down and burning the paper.

Forgetting is part of how a healthy memory works. It clears out what you don't need, so what matters can stand out. The goal is to remember the things you choose to remember.

Many people picture memory as a kind of video recording: something happens, your brain records it, and later you play it back. Research going back almost a century shows that's not how it works. Each time you remember something, your brain rebuilds it, and it can change in the process.

In 1932, the British psychologist Frederic Bartlett published a series of experiments in which people read a Native American folk tale called "The War of the Ghosts" and then retold it from memory, sometimes several times over months or years.

With each retelling, the story changed. People shortened it, dropped details that seemed strange to them, and changed parts to fit what made sense in their own culture. Bartlett concluded that remembering is an act of reconstruction.

Later research showed how easily memories can be shaped. In a 1974 study, Elizabeth Loftus and John Palmer showed people a film of a car accident and then asked how fast the cars were going when they "hit" each other, or when they "smashed" into each other.

A week later, people were asked whether they had seen broken glass in the film. There was no broken glass. But 32 percent of the people who had heard the word "smashed" said they had seen it, compared with 14 percent of those who heard "hit." Changing one word in the question changed what people remembered seeing.

In 1995, Loftus and Jacqueline Pickrell went further. With help from participants' family members, they described to people four events from their childhood. Three were real. The fourth, being lost in a shopping mall as a young child, never happened. About a quarter of the participants came to remember the false event, at least partly, and some described details of it.

This matters for anyone who wants to remember what they learn. It means your memory of what a book said, what a teacher taught, or what you decided in a meeting is less reliable than it feels.

Your mind fills in gaps and smooths over what you've forgotten without you noticing. The practical lesson is simple: when something matters, write it down accurately at the time, and go back to the source to check it, instead of trusting how sure you feel.

In 2009, Jeffrey Karpicke, Andrew Butler, and Henry Roediger surveyed college students about how they study. Rereading their notes or textbook was by far the most common strategy: 84 percent of students said they used it, and 55 percent said it was their main strategy. Testing themselves was much rarer. Only 11 percent said they used it, and just 1 percent said it was their main strategy.

That's a problem, because in 2013 a team of researchers led by John Dunlosky published a major review of ten common study techniques, looking at hundreds of studies to judge how useful each one was. They rated rereading and highlighting among the least useful. Summarizing also scored low. The two techniques they rated most highly were practice testing and spreading study out over time. In other words, the strategy most students in the survey relied on is one of the weakest, and the two strongest are among the least used.

Why do people keep rereading? Because of the difference between retrieval strength and storage strength from section 03. When you reread a page, it feels clear and easy, and that easy feeling seems like learning. Psychologists call this an illusion of fluency. The material is easy to recognize while it's in front of you, but that doesn't mean you'll be able to recall it on your own a week later.

Theo's way of studying for his certification was to highlight his textbook and then reread the highlighted parts the week before the exam. It felt productive. But on practice questions, he found he could recognize the right answer when he saw it and couldn't come up with it on his own.

One of the most powerful things you can do to remember something is to practice pulling it out of your memory: testing yourself, recalling it without looking, or explaining it from scratch. Our articles on mastery and on learning a language cover some of the classic studies. Here's one more that shows how strong the effect is.

In a 2011 study published in Science, Jeffrey Karpicke and Janell Blunt had students learn a science text in one of several ways. One of them was concept mapping, where students draw diagrams connecting the ideas in a text, which many teachers consider a deep way to learn. Another was retrieval practice: reading the text, then putting it away and writing down everything they could remember.

A week later, the students who practiced retrieval remembered more, even on questions that required them to make connections and draw conclusions, which is exactly what concept mapping is supposed to be good for. Retrieval works because pulling a memory out strengthens it. Recalling something checks whether you know it, and it's also one of the main ways you come to know it.

Our earlier articles explain why spreading review out over time beats cramming. The question many people have is how far apart to space it. In 2008, Nicholas Cepeda and his colleagues tested this with more than 1,350 people.

They taught everyone a set of facts, had them review the facts after a gap of anywhere from a few minutes to three and a half months, and then gave them a final test up to a year later.

The best gap depended on how long people needed to remember. When the final test was a week away, the best gap between learning and review was about one to three days. When the test was a year away, it was about three weeks to a month.

As a rule of thumb, the best gap was about 20 percent of the time until you'll need the information when that time is a few weeks, falling to about 5 percent when it's a year. The researchers also found that a gap that's too short hurts much more than a gap that's too long. If you're not sure, err on the side of waiting longer.

Many people practice one type of problem or topic at a time before moving to the next: ten problems of type A, then ten of type B. This is called blocked practice. The alternative is interleaving: mixing different types together, so you never know which kind is coming next.

In a 2007 study, Doug Rohrer and Kelli Taylor had college students practice finding the volume of different geometric shapes. One group practiced each kind of shape in a block, and the other mixed them together. During practice, the blocked group did better.

But on a test a week later, the interleaved group scored 63 percent while the blocked group scored 20 percent. Mixing forced students to figure out which method each problem called for, which is the skill a real test, or real life, requires.

The same thing works beyond math. In a 2008 study, Nate Kornell and Robert Bjork had people learn the painting styles of different artists by looking at examples. People who saw the paintings mixed together were better at identifying the artist of new paintings they'd never seen.

But most of them believed the opposite: they thought seeing one artist's paintings in a block had helped them more. Interleaving feels harder and less productive, even when it works better.

In a 1978 study, Norman Slamecka and Peter Graf found that people remembered words better when they had generated them themselves, for example by filling in a word from a clue, than when they simply read them. They called it the generation effect.

In practice, this means trying to answer a question, solve a problem, or predict what a chapter will say before you're told. Even if your first attempt is wrong, the effort of reaching for it prepares your mind to hold onto the right answer.

Testing yourself, spacing out reviews, mixing topics, and generating answers all make learning feel harder in the moment. Robert Bjork calls these desirable difficulties: kinds of difficulty that slow down how fast you seem to be learning but improve how much you remember in the long run. The struggle to retrieve something is what helps build storage strength.

The difficulty has to be one you can get through. Trying to recall something you never understood in the first place mostly leads to frustration. The goal is effort that leads to success, like recalling a fact that's hard but possible to remember, or solving a problem that stretches you but is within reach.

So when studying feels smooth and easy, you're probably not building much, and when it feels like work you can get through, you're probably on the right track.

In a well-known 1972 experiment, John Bransford and Marcia Johnson had people listen to a short passage and then try to recall it. Here's how it begins: "The procedure is actually quite simple. First you arrange things into different groups. Of course, one pile may be sufficient depending on how much there is to do."

Without any context, the passage is confusing, and people remembered little of it. But people who were told the topic before they heard it, that it was about doing laundry, understood it easily and remembered much more. Being told the topic afterward didn't help.

The point is that we remember what we understand, and we understand new information by connecting it to what we already know. The more connections a new idea has to your existing knowledge, the more ways there are to reach it later.

That helps explain why experts can pick up new things in their field quickly: they have a lot already in place for new information to attach to. When you learn something, it helps to ask how it relates to things you already know, where it fits, and what it reminds you of.

One easy way to process information more deeply is to learn it as if you'll have to teach it. In a 2014 study, John Nestojko and his colleagues had people study a passage. Some were told they'd be tested on it, and others were told they'd have to teach it to someone else.

In the end, nobody taught anyone, and everyone took the same test. The people who expected to teach remembered more, and their recall was better organized, with more of the main points. Expecting to teach seems to make people sort out what matters and how it fits together.

People tend to remember things they're curious about. In a 2014 study, Matthias Gruber, Bernard Gelman, and Charan Ranganath at the University of California, Davis, had people rate how curious they were about the answers to a list of trivia questions.

Then, while the people waited a few seconds for each answer, the researchers showed them a photo of an unrelated face. People remembered more answers to questions they were curious about.

They also remembered the unrelated faces better if they had seen them while they were curious, and the effect was still there a day later. It was a small study of 19 people, but it suggests that being curious puts the brain in a state where it holds onto information better.

You can use this on purpose. Before you start reading or studying something, write down a few questions you want answered. Look for the part of the subject that actually interests you. A question you genuinely want answered can be a strong memory aid.

Emotion has a similar effect. Researchers including James McGaugh have shown that emotionally arousing experiences tend to be remembered better, because the brain's emotional systems help strengthen the memory as it's being stored. In one 1995 study, Larry Cahill and McGaugh told people a story with slides.

For some, the middle of the story was neutral. For others, it described a boy badly injured in an accident. Two weeks later, people who heard the emotional version remembered the middle of the story much better. You can't make every lesson dramatic, but you can connect what you learn to something that matters to you, like a goal, a problem you care about, or a real person who'll benefit.

Theo started applying this. Before reading each chapter of his certification textbook, he wrote down two questions about how it applied to a real problem at work. Instead of reading to get through the chapter, he was reading to answer something he cared about.

In a classic 1975 study, Duncan Godden and Alan Baddeley had scuba divers learn lists of words, either on the beach or about 20 feet underwater. Then they tested the divers either in the same place or the other place.

Divers remembered more when they were tested in the same environment where they had learned, whether that was underwater or on land. The place itself had become part of the memory.

This is called context-dependent memory, and it's part of why a song can bring back a whole summer. It also means that if you always study in one place, you may have a harder time recalling the material somewhere else, like in an exam room or a meeting.

Two findings help. First, in a 1978 study, Steven Smith, Arthur Glenberg, and Robert Bjork found that people who studied the same material in two different rooms remembered it better than people who studied it twice in the same room.

Varying where you study seems to make memories less tied to one place. Second, in a 1979 study, Smith found that people tested in a different room from where they had learned did better when they were asked to picture the original room first. So if you're struggling to remember something, try mentally putting yourself back where you learned it.

Every year, people compete in memory championships, memorizing hundreds of random numbers or the order of a shuffled deck of cards in minutes. It's natural to assume they have special brains. In a 2003 study, Eleanor Maguire and her colleagues compared top memory competitors with ordinary people.

They found no difference in general intelligence and no difference in brain structure. What they did find was that nine out of ten of the champions used the same strategy: the method of loci.

In 2017, Martin Dresler and his colleagues tested whether ordinary people could learn it. They had people with no memory training practice the method of loci for 30 minutes a day for about six weeks.

Before training, they could recall an average of about 26 words from a list of 72. After training, they averaged about 62. Four months later, without any further practice, they were still remembering far more than when they started.

Pick a place you know very well, like your home. Choose a route through it, with a series of specific spots along the way: the front door, the hallway table, the couch, the kitchen sink, and so on.

To memorize a list, picture each item at one spot along the route, as vividly and strangely as you can. If the first item is "eggs," you might picture eggs cracking all over your front door. To recall the list, walk the route in your mind and see what's at each spot.

The method works because people have strong memory for places and images, so it uses those strengths to hold information that's otherwise hard to keep, like a list. It's best for things that need to be remembered in a specific order, like the points of a speech, a list of steps, or a sequence of facts. It's less useful for understanding ideas, which depends on meaning and connection, as section 07 explained.

Since working memory can only hold a few chunks at a time, another technique is to make each chunk bigger. A string like 1-9-4-5-1-9-6-9 is eight numbers, but if you notice it's the years 1945 and 1969, it's two. Grouping information into meaningful pieces is one of the main ways experts handle large amounts of information.

Names are one of the hardest things for many people to remember, and research explains why. In a 1987 study, Kathryn McWeeny and her colleagues showed people photos of faces and told them a name and a job for each. Some people learned that a person's name was Baker. Others learned that the same person was a baker.

People were much better at remembering that someone was a baker than that someone was named Baker, even though it's the same word. The job connects to a lot of things you know, like bread, an apron, and early mornings, while the name connects to almost nothing. When you meet someone, you may be busy thinking about how to introduce yourself, so their name may never get properly encoded.

Putting the research together, here's how to remember names. Pay attention the moment you hear it, instead of planning your own introduction. Repeat it back right away ("Nice to meet you, Maria"). Connect it to something meaningful, like someone else you know with the same name or a vivid image the name suggests. And retrieve it later in the conversation and again afterward, the same way you'd space out any review.

Memory champions are one kind of expert. But plenty of people memorize huge amounts of material as part of their work or their faith, and the way they do it lines up closely with the research in this article.

The question actors hear more than any other is "How do you learn all those lines?" The psychologist Helga Noice and her husband, the actor and theater professor Tony Noice, spent more than two decades studying the answer. They found that most professional actors don't learn lines by repeating them over and over.

Instead, they break the script into what actors call beats: small units, each defined by what the character is trying to do or get from the other person in that moment. They work out why the character says each line, what it means, and what it's meant to do to the other person.

Once they understand that, the exact words become much easier to remember. Tony Noice summed it up this way: actors "don't memorize material, they make material memorable."

The Noices called the underlying principle active experiencing: using physical, mental, and emotional effort to communicate the meaning of material to another person, real or imagined. When they taught it to college students, the students who studied a text by imagining explaining its meaning to someone who needed it remembered more than students who memorized it by rote.

They also found that lines learned while making a fitting movement, like crossing the stage, were remembered better later, even when the movement wasn't repeated.

And when they gave adults in their sixties to nineties a four-week course in acting, those adults improved in word recall and problem solving compared with both a group that took a visual arts course and a group that took no course.

Actors use the same principle as the laundry passage and the expecting-to-teach study. If you need to remember something word for word, like a speech, a pitch, or an important explanation, start by working out what each part is for and what you want it to do to the person hearing it, before you try to memorize the words.

To get a license to drive one of London's black cabs, drivers have to pass a test known as The Knowledge. It requires learning the roughly 25,000 streets within six miles of Charing Cross, along with thousands of landmarks, and being able to work out routes between any two points from memory. Most people who succeed spend three to four years studying.

In a 2000 study, Eleanor Maguire, who also led the memory champion study in section 09, scanned the brains of experienced London cab drivers. The back part of their hippocampus, an area important for memory of places and routes, was larger than in people who weren't cab drivers, and the longer someone had driven a cab, the larger it was.

That could have meant people with a larger hippocampus were more likely to become cab drivers. So in a later study, Katherine Woollett and Maguire followed trainees over the years they studied for The Knowledge. Those who qualified showed growth in that part of the hippocampus. Those who failed or quit, and a comparison group who never trained, didn't. Years of learning had changed the physical structure of their brains.

Many Muslims around the world have memorized the entire Quran, which has more than 6,000 verses. A person who has done it is called a hafiz. The traditional method, which many begin in childhood, combines memorizing a small new portion each day, reciting it aloud many times, and reviewing what's already been learned on a regular schedule so it isn't lost.

Similar traditions of memorizing scripture by recitation have existed for centuries among Jewish students of the Hebrew Bible and in the Vedic tradition in India. The approach is close to what the research recommends: small portions, active recall out loud, and steady review spaced over time.

Long before most people could read, poets performed epic stories from memory. In the 1930s, the Harvard scholar Milman Parry, and later his student Albert Lord, recorded traditional singers in what was then Yugoslavia who could perform epic poems thousands of lines long. One of them, Avdo Međedović, performed a single poem of more than 12,000 lines.

The singers weren't reciting fixed texts word for word, and each performance was somewhat different. They knew the story's structure and had a large stock of ready-made phrases and scenes, which Parry called formulas, that they fit together as they sang.

Parry argued that Homer's Iliad and Odyssey were built the same way, which is why they repeat phrases like "rosy-fingered Dawn." It's close to the chunking from section 09, and a reminder from section 04 that memory rebuilds instead of replaying.

Concert pianists play long, complicated pieces from memory. In a study published in 2002, the psychologists Roger Chaffin and Gabriela Imreh tracked how Imreh, a concert pianist, learned a fast movement of Bach's Italian Concerto over many hours of practice.

She organized her memory around the structure of the piece, its sections and the places where they changed, and chose specific points to think about while playing, which the researchers called performance cues. Those cues gave her places in the music she could reliably return to, much like the spots along a memory palace route.

Put together, these experts point to the same few principles as the research: understand what you're learning and why each part is there, organize it into a structure you can move through, practice recalling it actively and out loud, and keep reviewing it over time.

An important part of the work of storing a memory happens after you've finished learning, while you sleep. In a 2006 study, Steffen Gais, Brian Lucas, and Jan Born had high school students learn English vocabulary.

Students who went to sleep within a few hours of learning remembered more than students who stayed awake longer before sleeping, regardless of the time of day they studied.

Students who missed a night of sleep after learning remembered less, and the effect was still there even after they had a night of recovery sleep. If you're learning something important, studying in the evening and then getting a full night's sleep is one of the simplest ways to help it stick.

Exercise affects the part of the brain most involved in forming new memories, the hippocampus. In a 2011 study, Kirk Erickson and his colleagues had 120 older adults either walk for 40 minutes three times a week or do stretching and toning exercises, for a year.

In the walking group, the hippocampus grew by about 2 percent. In the stretching group, it shrank by about 1.4 percent, which is roughly what's normal with age. The walkers' memory improved along with it.

Stress can block recall when you need it most. In a 2000 study, Dominique de Quervain and his colleagues gave people a dose of cortisone, which raises levels of the stress hormone cortisol, an hour before testing their memory of words they had learned the day before. Those people recalled fewer words than people given a placebo.

That fits a common experience: knowing something cold, then blanking on it in a high-pressure moment. Retrieval practice may help here too. In a 2016 study, Amy Smith, Vanessa Floerke, and Ayanna Thomas found that people who had learned material by testing themselves remembered it just as well after a stressful task, while people who had learned it by restudying remembered less under stress.

Practicing recall, ideally under conditions that feel a little like the real thing, like answering practice questions under a time limit, is a good defense.

Many people assume memory simply gets worse after a certain age. The picture is more mixed than that. In 2015, Joshua Hartshorne and Laura Germine analyzed test results from tens of thousands of people of different ages.

Different abilities peaked at very different times. The speed of processing information peaked around 18 or 19. Short-term memory for names peaked in the early 20s, and memory for faces in the early 30s.

But vocabulary and general knowledge kept improving, and didn't peak until the late 60s or early 70s. Some kinds of quick memory do decline with age, but what you know can keep growing, and the habits in this article, along with sleep and exercise, help at every age.

Encoding needs attention. In a 1996 study, Fergus Craik and his colleagues had people learn words while also doing a second task at the same time. Dividing their attention while learning significantly reduced how much they remembered later.

When you read with your phone buzzing, half-watch a lecture while answering messages, or skim a book while thinking about something else, much of the information is never encoded at all. Our article "How to Focus" covers how to protect your attention.

You don't need to remember everything. With notes, books, search engines, and phones, a lot of information is easy to look up when you need it. But there's a cost to relying on outside storage without thinking.

In a 2014 study, Linda Henkel had people take a tour of an art museum. They photographed some objects and only looked at others. The next day, they remembered fewer of the objects they had photographed, and fewer details about them, than the ones they had just looked at.

It was one study, but the idea fits the rest of this article. When you hand something off to a device, your mind may treat it as something it doesn't need to keep.

So it helps to decide on purpose what to keep in your head and what to keep elsewhere. A good rule: store facts you only need occasionally, like dates, phone numbers, and detailed procedures, outside your head, in notes you can find.

Keep in your head the ideas, principles, and knowledge you think with, the things you need to have ready in a conversation, a meeting, or a decision, and the foundations that new learning in your field will connect to. That's the knowledge that makes you better at what you do.

Here's how to put everything in this article together, for a book, a course, a training, or anything else you want to remember.

Here's how it changed things for Theo. He stopped highlighting and rereading. For each chapter of his certification textbook, he wrote two questions about his work before reading, read without his phone, then closed the book and wrote down everything he could remember.

He turned key terms into flashcards and reviewed them in Anki for 15 minutes each morning. Every Sunday he took a mixed set of practice questions from all the chapters he'd covered so far. The first few weeks felt slower and harder than his old way of studying.

On his practice exams, his scores went from the low 60s to the mid 80s, and he passed the certification on his first try. He started doing the same with the books he read for himself: after each one, he wrote a page from memory on its main ideas and how he'd use them, and reviewed those pages once a month. Six months later, he could explain the main ideas of most of the books he'd read that year.