Why reviewing doesn't work (but does, once you change the timing)
For most of us, the first method that comes to mind for learning something is reading it over and over: going through your lecture notes three times start to finish, reviewing an article again and again, looking back at the sentences you underlined over and over.
The problem is that this method makes you feel like you're learning far more than you actually are. When you read a text for the fifth time, the sentences feel "familiar," they glide past your eyes smoothly, and that fluency sends your brain a signal that says "you know this." But feeling familiar with something and actually remembering it are not the same thing. Once you close the book, can you recall that information from scratch, with no cues at all? Most of the time, the answer is no.
Reviewing at the right time
Imagine you're trying to memorize a friend's new phone number. You have two options:
- Repeat the number ten times a day, every day.
- Learn the number, then look at it again right when you feel yourself starting to forget it. Wait a bit longer the next time. Extend the wait a little more with every successful recall.
The second method produces a far more durable result with far fewer repetitions. The reason is simple: when your brain is forced to recall a piece of information right as you're on the verge of forgetting it, it re-encodes that information more strongly. If you review too early, while the information is still fresh, the effort barely helps because your mind was never really challenged. If you review too late, you've already lost the information and you're learning it from scratch.
So what really matters isn't "how many times you review," it's "when you review." This idea is called spaced repetition: extending the interval before the next review a little more after every successful recall. We go deeper into the research behind this approach in The Science.
So how do you track this by hand?
Keeping track of "when do I need to review this" in your head for dozens of topics is practically impossible. This is exactly where flashcards come in.