Review Should Feel Challenging

It's the act of successfully retrieving fuzzy memory, not clear memory, that extends the memory duration.

Students often expect review to be easy.

At least part of this expectation is due to conditioning: in school, when the teacher says it’s a “review day,” they might as well call it an “off day.”

But if you’re actually trying to maximize learning efficiency, then reviews should feel tough.

Why? Because recalling tricky information improves memory, while recalling easy information doesn’t.

That’s the whole idea behind spaced repetition: your memory has to get a bit fuzzy before the next repetition, otherwise the desired effect – slowing the rate of forgetting and remembering longer next time – doesn’t happen (or at least not nearly as much). It’s the act of successfully retrieving fuzzy memory, not clear memory, that extends the memory duration.

And if review problems are easy, not actually extending your memory duration, then what’s the point? It’s better to learn something new.

A maximum-efficiency teacher will intentionally let your memory fade a bit before review so that the act of refreshing your memory actually deepens your long-term encoding, and they’ll use the extra time to cover more new material.

Desirable Difficulties

In general, learning requires introducing “desirable difficulties” into the recall process, making it tough yet achievable.

During an initial lesson, the desirable difficulty comes from manipulating new information. During review, the desirable difficulty comes from successfully recalling fuzzy memory – you’ve already learned how to manipulate the information, but now you’re practicing in a trickier setting where enough time has passed for your memory to fade.

Consequently, reviews should feel as mentally taxing as initial lessons. You’re getting better, but the bar for success also is getting higher. Your brain has to hold the memory for a longer period of time – just like a muscle holding a weight.

Analogy to Weightlifting

The analogy to weightlifting runs deep.

In the context of spaced repetition, the way you increase the weight is by waiting longer before retrieving the knowledge again. But you also don’t want to wait too long to retrieving the knowledge, because then you won’t be able to successfully retrieve it.

This is just like how in weightlifting, you need to increase the weight to the point where you struggle to lift it, but you are able to overcome the struggle. That’s how you build muscle, and that’s also how you build long-term memory.

Spaced repetition = “wait”lifting.