Skip to content
Published on

Learning by Teaching: Follow Lectures, Then Build Your Own

🇰🇷KO🇺🇸EN🇯🇵JA
Split View필사 모드
Authors

Introduction: I learned more deeply because I wanted to teach

For a while, I wanted so badly to explain the physics of spin on a table tennis forehand drive that I ended up staring at racket angle and impact timing far longer than I ever stared at my own swing.

At first I just wanted to play well. But when a partner I practiced with asked, "How do you put that spin on the ball?", my mouth froze. My hand clearly knew how to do the motion, yet when I tried to put it into words, not a single sentence came out smoothly.

After that day, a strange ambition took hold of me. The ambition was simple: the next time I got the same question, I wanted to explain it cleanly. Because of that ambition, I watched lectures on YouTube, looked up the physics of spin, and filmed my own swing to compare. I learned far faster and far more deeply than I ever did when I only wanted to play well.

This experience repeated itself exactly the same way in coding. The topics I resolved to write up on our internal wiki were always the topics I ended up understanding most firmly. Conversely, the topics I waved off with "I sort of get it" eventually collapsed during an interview or an incident.

This piece is a record of how to turn the urge to teach into an engine for learning. Rather than abstract motivation, I want to lay out the concrete process of following lectures and building things yourself, the moment of discovering your own gaps mid-explanation, and the humility needed to guard against teaching badly.

1. The urge to teach is the most honest engine of learning

Why "I want to explain it" is stronger than "I want to be good at it"

The desire to "be good at something" is vague. The bar for what counts as good is blurry, and a passable imitation can be enough to feel satisfied. The desire to "explain it," by contrast, is brutally honest, because the listener's face is your scorecard.

The moment you begin to explain, you confront the boundary between what you truly know and what you only thought you knew. Concepts that were faintly connected in your head reveal themselves, the instant they leave your mouth, like a broken bridge.

I call this "explanation debt." Like technical debt, a concept you understood only roughly comes back, the moment you have to explain it, with interest tacked on.

The three faces of the desire to teach

The urge to teach is not a single thing. At least three motives are mixed into it.

  • The desire for recognition: I want to show what I know.
  • The desire to organize: I want to tidy up the inside of my head.
  • The desire to contribute: I want to save someone else's time.

If only the desire for recognition remains, teaching becomes showing off. When the desire to organize and the desire to contribute are also alive, teaching becomes a tool for learning. That is why checking your motives matters.

2. The protege effect: you learn better when you teach

What the research says

Psychology calls the phenomenon where "the person teaching learns more than the person being taught" the protege effect.

As is well known from John Hattie's meta-analysis, explaining to and teaching peers belongs to the cluster of activities with large learning effects. In addition, active learning studies repeatedly confirmed in the learning sciences show that the effect of active learning, where you explain and retrieve, is greater than passive learning where you merely listen.

There are two key mechanisms here.

  1. The generation effect: information is remembered better when you produce it yourself than when you simply receive it.
  2. Retrieval practice: the very act of pulling information out of your head strengthens memory. Teaching is, in effect, high-intensity retrieval practice.

Teaching is "organized retrieval"

Memorizing words with flashcards is also retrieval practice. But teaching adds the further burden of "structuring."

To explain something to someone, you have to arrange information in order, connect cause and effect, and attach examples. In this process we go beyond merely remembering facts and are forced to organize the relationships between concepts.

While trying to explain database indexes to a junior developer, I realized that I myself only had a fuzzy grasp of "why an index degrades write performance." While preparing the explanation, I studied the update cost of a B-tree again, and only then did my understanding become solid.

3. Following lectures: imitation is not a shameful stage

Why not build from scratch right away

The saying "you only grow real skill by building something right away" is only half true. If you try to make something out of nothing with no scaffold at all, most people are crushed by the blankness and cannot even start.

Following a lecture is a kind of training wheels. You borrow the order and structure an expert has already organized, and you simply go around the loop once, all the way to the end. The experience of going all the way around is itself a huge asset.

Three rules that turn following along into learning

The problem is that following along easily degenerates into copy-paste. Your hands move, but your head falls asleep. There are three rules to prevent this.

  1. Predict one unit ahead: pause for a moment and predict what the instructor will do next before pressing play. The point where your prediction missed is exactly the point of learning.
  2. Add one variation: follow the lecture faithfully, but change one thing, such as a variable name or the example data. Even a small variation wakes up your active engagement.
  3. One line of notes in your own words: when each step ends, write a single line on "why this step is needed."

A checklist for the following-along stage

[ ] I completed the lecture once, all the way to the end
[ ] I predicted the next action just before each step
[ ] I varied the example in at least one place
[ ] I noted the reason for each step in my own words
[ ] I separately recorded the points where I got stuck
[ ] I asked myself whether I could turn off the lecture and rebuild from the start

The last item is the key. If you can rebuild even with the lecture turned off, only then are you ready to move on to the next stage.

4. Building it yourself: leaving the lecture for your own problem

From imitation to variation, from variation to creation

It is similar to the process of learning music. At first you play the score exactly as written (imitation). Next you change the key or tweak the rhythm a little (variation). Finally you make your own piece (creation).

Learning traces the same curve.

  • Imitation: build exactly what the lecture builds.
  • Variation: change part of the lecture to fit your situation.
  • Creation: solve your own problem that the lecture never covered.

Many people stop at imitation. The state of having listened to a hundred lectures yet being unable to build anything is exactly this. Only when you cross over into variation and creation does the knowledge become your own.

How to find "your own problem"

The biggest difficulty of the creation stage is deciding what to make. The following questions help.

  • What annoying task do I repeat all the time?
  • What is lacking in the tools I use often?
  • What does a friend or colleague find inconvenient?

Because organizing foreign-language vocabulary every day was a chore, I built a small vocabulary tool using the web technology I learned in a lecture. It was a feature the lecture never had, but it was precisely in the process of filling that missing part that I learned the most.

Imitation-variation-creation comparison table

StageGoalSafety netDepth of learningMain risk
ImitationExperience of finishingThe whole lectureShallowDegenerating into copy-paste
VariationPartial changeThe lecture skeletonMediumVariation too timid
CreationSolving your own problemAlmost noneDeepFrustration from too big a goal

The risk of the creation stage is too big a goal. It is good to deliberately keep your first creation small.

5. Discovering gaps through explanation: the Feynman technique

The four steps of the Feynman technique

There is a learning method named after the physicist Richard Feynman. The core is to try explaining something so even an elementary school student can understand.

  1. Pick the concept you want to learn.
  2. Write it on paper as if explaining to someone who knows nothing.
  3. Mark the points where you get stuck or start to mumble. Those are exactly the gaps.
  4. Study those gaps again, and refine the explanation with analogies and examples.

The power of this technique lies in step 3. The point where an explanation gets stuck does not lie. The ignorance we had hidden behind difficult words is laid bare the moment we try to unravel it in plain language.

Jargon can be a hiding place for ignorance

We often pretend to understand by stringing together difficult terms. Saying "this is really just non-blocking I/O based on an asynchronous event loop" makes you look smart. But the moment you try to explain to a seven-year-old "why does it look like one person is doing several things at once?", whether you truly understood is revealed.

A good explanation is the work of turning hard words into easy ones. The point where that translation fails is exactly the point you need to learn.

6. Producing output as content: blog, video, presentation

Output turns private organizing into public responsibility

Organizing in your head and organizing in writing are different. Writing gets read again. So you cannot get away with passing over it loosely.

Output such as blog posts, short videos, or internal presentations gives learning a public responsibility. The pressure of "what if someone reads this and believes something wrong?" makes us verify one more time.

Characteristics by output format

FormatStrengthCostSuitable situation
Blog postSearchable, easy to editWriting timeOrganizing concepts
Short videoStrong for demonstrating motionEditing burdenHand motions, demos
Internal presentationImmediate feedbackSchedule coordinationSharing with the team
One-on-one explanationThe most honest feedbackNeeds the other person's timeDeep check

The trap of output: organizing only, never building

Output has its own trap too. The state of having written a hundred blog posts yet having not a single work of your own. Output is a supporting tool that solidifies learning; it does not replace building. Building and output must take turns.

7. Feedback: the real test of teaching

Teaching without feedback is a monologue

The value of teaching is decided by whether the listener understood. So feedback is not optional but essential.

The best way to get feedback is to receive questions. A good question reveals an angle we never thought of. A single line like "but in this case, what happens?" pokes precisely at the hole in our explanation.

Techniques of explanation that invite feedback

  • Deliberately leave it unfinished: if you honestly say "I am not sure about this part either," questions pour in.
  • Provoke with examples: a concrete example invites counterexamples. A counterexample is the best feedback.
  • Grant the right to be wrong: a single line like "I could be wrong, so feel free to point it out" changes the mood.

How to receive feedback

If you take feedback defensively, you learn nothing. You need to practice receiving criticism as data rather than as a personal attack. The moment you say "ah, I missed that part, thank you," teaching becomes learning again.

8. Guarding against teaching badly: the place for humility

The first peak of Dunning-Kruger

The Dunning-Kruger effect in psychology is well known. It is the phenomenon where someone who has just started learning is, of all things, the most confident. When you know only a little, you most want to talk.

This risk always tags along with teaching. When someone with a shaky grasp confidently teaches something wrong, it harms the listener. A wrong mental model is harder to correct later.

Principles of responsible teaching

Humility does not mean do not teach. It means teach responsibly.

  • Distinguish certainty from guesswork: clearly separate "I am sure" from "I think."
  • State your sources: say together where you learned it and what the basis is.
  • Say you do not know when you do not: "I do not know that. Shall we look it up together?" is not a shameful thing to say.
  • Stay open to correction: if you taught something wrong, correct it quickly.

The mindset of someone who learns by teaching

The ideal attitude of someone who learns by teaching is the stance that I am merely someone who learned it first. I am not someone who knows the right answer; I am someone who wandered one step ahead, and I share the path I wandered. This attitude makes the teacher a companion rather than an authority.

9. A practical roadmap: learning by teaching over 30 days

Week 1: following along and predicting

  • Complete one lecture on a topic you want to learn, all the way to the end.
  • Predict the next action just before each step.
  • Separately record the points where you got stuck.

Week 2: variation and explanation

  • Vary the lecture's examples to fit your own situation.
  • Explain one core concept on paper using the Feynman technique.
  • Study again the gaps where your explanation got stuck.

Week 3: creation and output

  • Pick one small problem of your own that the lecture never covered, and build it.
  • Organize the process you went through into one blog post.
  • Deliberately leave an unfinished part.

Week 4: teaching and feedback

  • Explain one-on-one to a colleague or friend.
  • Record every question and counterexample you received.
  • Correct the parts that were pointed out and update your post.

A daily five-minute routine

One-line summary of what I learned today:
The point where my explanation got stuck today:
The gap I will fill tomorrow:

This five-minute routine is small, but when a month of it accumulates, your own learning patterns become visible.

10. Case study: an internal presentation at LINE

Back when I worked at LINE, I was once put in charge of a presentation to share a newly introduced message queue system with my team. At first I thought, "It is a system I operate, so of course I know it well."

But while making the presentation slides, points where I got stuck kept coming up. "Why does this queue guarantee message order, but that one does not?", "What exactly is the relationship between retries and idempotency?" I was operating it, but when I tried to explain the principles in words, gaps showed up everywhere.

The night before the presentation, I reread the documentation, tested the behavior myself, and explained it once in advance to a colleague. I learned far more in the process of preparing the presentation than in the presentation itself. The question an audience member threw out, "So what happens when there is an incident?", let me see a scenario I had not even considered.

There are three lessons I took from this experience.

  • Being able to operate something and being able to explain it are different.
  • The process of preparing a presentation is a bigger learning than the presentation itself.
  • The audience's questions illuminate exactly my blind spots.

A moment of teaching, seen as dialogue

The following is a scene from a conversation in which I was explaining cache invalidation to a junior colleague.

Junior: Why do people say cache invalidation is hard?
Me: Hmm... when the data changes you have to clear the cache too,
    but deciding when to clear it is tricky.
Junior: Then why not just clear it every time the data changes?
Me: (pausing for a moment) ...uh, in a distributed environment it is
    not easy to clear the caches on several servers at the same time...
Junior: And what happens if you cannot clear them at the same time?
Me: (pausing again) ...wait, let me organize that and get back to you.

That hesitation was the starting point of my learning. The junior's naive questions poked precisely at the point I "believed I knew but was actually fuzzy on." Teaching is, in this way, the fastest path to discovering your own ignorance.

11. The cognitive principles of learning by teaching

Why output is stronger than input

There is a concept in cognitive psychology called "desirable difficulties." This idea, well known from Robert Bjork's research, holds that long-term memory is actually strengthened when there is appropriate difficulty in the learning process.

Teaching is a textbook desirable difficulty. Pulling information out of your head (retrieval), organizing it in order (structuring), and turning it into plain language (translation) are all cognitively hard. That very hardness is what makes learning solid.

Conversely, passively listening to a lecture is easy. Because it is easy, it does not stick well. This is exactly why we listen to a lecture and feel we "understood" yet cannot actually use it.

Elaboration: making connections

When we teach, we connect new knowledge to existing knowledge. This is called elaboration. An analogy like "this is just like a librarian finding a book for you" is one form of elaboration that connects a new concept to something familiar.

Good teaching produces good analogies. And in the process of making good analogies, the teacher's understanding deepens the most.

12. Common mistakes in learning by teaching

Mistake 1: trying to teach only after becoming perfect

Many people put it off, saying "once I know enough, I will teach then." But the day you know enough never comes. That is because teaching is not proof of completion but a process of learning.

In fact, there is a unique advantage when someone who just learned teaches. Experts become so familiar that they often forget where a beginner gets stuck. This is called the curse of knowledge. Someone who just wandered that very path knows best the heart of someone who is wandering.

Mistake 2: not considering the audience

The same content has to be explained completely differently depending on the listener. The explanation you give an expert and the one you give a beginner have to differ. An explanation that does not consider the audience either too hard or too trivial reaches no one.

The first question of good teaching is "what does this person already know, and what do they not know?" To answer this question you have to stand in the other person's place. So teaching is also a training in empathy.

Mistake 3: turning away from feedback

If you do not check "did it get across well?" after teaching, you repeat the same mistake. A face that did not understand, a misguided question, a misapplied attempt are all precious feedback. If you turn away from them, teaching stays a one-sided monologue.

Mistake 4: piling up input only, never producing output

Even if you listen to a hundred lectures, if you never once build or explain, the knowledge remains someone else's. The core of learning by teaching is balance. You have to take turns between input and output, following along and building, learning and teaching.

Summary of the learning loop

1. Input: borrow a skeleton from a lecture or book
2. Follow along: go around the loop once (while predicting)
3. Variation: change part of it to fit your situation
4. Creation: solve your own small problem
5. Explanation: find the gaps with the Feynman technique
6. Output: create public responsibility via post, video, talk
7. Feedback: reduce blind spots with questions and counterexamples
8. Correction: fix what was wrong and back to step 1

These eight steps are not a straight line that runs once and ends, but a spiral that keeps turning. Each time you go around the loop, understanding deepens by one more layer.

Frequently Asked Questions (FAQ)

What if there is no one around to teach?

The target of teaching does not have to be a person. Explaining to an empty chair, a doll, or your future self also works. The key is to explain out loud, or in writing, from start to finish. Going further, writing a post in an anonymous community is also a good method.

I am still a beginner; is it not a nuisance to teach?

There is a unique advantage when a beginner teaches a beginner. Someone who just wandered knows best the heart of someone who is wandering. You only need to keep the principles of distinguishing certainty from guesswork, stating your sources, and correcting yourself when wrong.

Between building and following lectures, which should I do first?

If you are a complete beginner, grabbing a skeleton by following along reduces frustration. But do not linger too long in following along. Once you have gone around the loop to the end, it is good to move quickly into variation and creation.

If I write a blog and no one reads it, is it meaningless?

Even with no views, the learning effect stays the same. The primary beneficiary of output is the writer. That said, if even one person reads it and is helped, that is a bonus reward that follows along.

Does teaching not actually cut into my own study time?

In the short term it can feel that way, because preparing an explanation takes time. But that time is not waste; it is the most concentrated learning time. Even within the same hour, an hour spent preparing an explanation sticks far more deeply than an hour spent reading passively. It is more accurate to see it as the quality of time changing rather than the time shrinking.

What topic is good to start learning by teaching with?

A topic you use most often right now yet only know vaguely is a good starting point. A frequently used topic keeps your motivation alive, and a vaguely known topic exposes its gaps well when you explain it. Rather than too grand a topic, start with a small topic you can organize into one short post.

Closing: the fastest path to learning is to share

I learned table tennis spin more deeply because I wanted to explain it, I discovered my own ignorance while trying to teach indexes, and I crossed beyond the lecture while building a vocabulary tool. The common thread is one. I learned better when I tried to share than when I tried to swallow it alone.

Teaching is not a seat of authority. Teaching is the most honest mirror. Where an explanation gets stuck, we see our own gaps; where we receive a question, we see our own limits. And the process of filling those gaps and limits is the fastest learning there is.

Pick one thing you learned today and try explaining it to someone in a single paragraph. That point where you get stuck is the place where tomorrow's you will grow the fastest.

References

Discuss on Twitter • View on GitHub