Spaced repetition: the method to never forget a lesson again
May 28, 2026
You learned your lesson yesterday. This morning, you know 70% of it. In 3 days, 40%. In a week, 15%.
It's not you. That's just how your brain is designed. A German named Ebbinghaus demonstrated this over 130 years ago: it's the forgetting curve.
But there's a hack to counter it. And it's called spaced repetition.
What is spaced repetition
It's the art of reviewing information just when your brain is about to forget it. Not before, not after.
Each time you review it at the exact right moment, the memory trace gets stronger. And the interval before the next forget becomes longer. And longer. And longer.
The result: after 4-5 well-timed repetitions, you retain the information for years.
It's the method used by all medical students, polyglots, and memory champions. Not because it's sexy. Because it's what works.
The principle in 1 mental scheme
Imagine your memory is a wooden wall.
Every time you learn something, you drive a nail in. If you do nothing, the nail falls out.
If you hit the nail again at just the right moment, it goes in a little deeper. If you hit it again, it goes in further.
By timing your strikes well, the nail is driven in forever.
That's exactly how spaced repetition works with your memory.
The classic intervals (2357 method)
A simple and effective routine, notably used by British universities:
Day 0: you learn the lesson
Day 1: 1st review (10 min)
Day 3: 2nd review (10 min)
Day 7: 3rd review (10 min)
Day 14: 4th review (5 min)
Day 30: 5th review (5 min)
Total: less than an hour of review spread over a month for a long-term memorized lesson.
Compare that to: cramming for 4 hours the night before the exam and forgetting everything 2 weeks later. You get the idea.
Why spaced repetition beats cramming
Cramming = storing in short-term memory. You barely pass the exam, and you forget 90% within a week.
Spaced repetition = storing in long-term memory. You pass the exam and you finish your studies still knowing what you learned.
Concrete difference: with spaced repetition, your first-year classes still serve you in your master's program. With cramming, you have to relearn everything every single time.
How to apply spaced repetition in practice
Option 1: Old-school (paper)
You write the date of each review on your flashcards. During each session, you test yourself (active recall), check it off, and schedule the next one.
Advantage: free. Disadvantage: you have to keep the tracking board up to date for every chapter. Quickly becomes a nightmare if you have 10 subjects.
Option 2: Anki
The benchmark app. Powerful SM-2 algorithm. But brutal learning curve, outdated interface.
Option 3: Koro AI
You upload your course, the AI generates flashcards, and the system handles the spaced repetition all by itself. It tells you what to review today, without you having to calculate a thing.
It is designed for students who want the benefits of spaced repetition without the headache of configuration.
The most common mistakes
Reviewing too early. If you review your lesson every 24 hours, your brain gets bored and learns nothing new. You have to wait until you are about to forget — that's where the magic happens.
Reviewing too late. If you wait 3 weeks before reviewing, you've forgotten everything. You start back from scratch. It's no longer repetition, it's initial learning.
No active recall. Spaced repetition without testing is just rereading. You must test yourself, not reread. Otherwise, it is ineffective.
The same for everyone. A simple piece of information is quickly engraved, a complex piece of information requires more repetitions. Adjust the intervals according to what you struggle with.
The magic combo: active recall + spaced repetition
Active recall makes you learn (by testing you). Spaced repetition makes you retain (by timing the tests).
The two together are the most effective memorization method in the world, period. All cognitive science research has confirmed this for 50 years.
This is exactly what Koro AI sets up automatically: you upload your course, you test yourself on the generated flashcards, and the app brings back what needs to be reviewed at the right time.
You do zero calculations. You just do the sessions. You retain.
Conclusion
Your brain forgets 85% of a lesson within a week. Spaced repetition fights back by making you review right at the moment you were going to forget. Combined with active recall, it is the most powerful method in the world for long-term memorization. The 2357 routine (D1, D3, D7, D14, D30) is enough to retain everything with 1 hour per month per course.