Spaced repetition is so similar to weight training that it might as well be called “wait” training.

The fuzzier that memory, the harder it is to lift. The wait creates the weight.

Spaced repetition is so similar to weight training that you might as well call it wait training.

You’re lifting a memory off the floor of long-term memory and raising it up into working memory.

The fuzzier that memory, the harder it is to lift. The wait creates the weight.

And just like successfully lifting a heavy weight strengthens muscles, successfully recalling a fuzzy memory (lengthy wait) strengthens memory.

But you have to retrieve from memory. Spaced “re-reading” doesn’t count – that’s like letting your spotter lift the weight for you.

(The movement you’re trying to train is the lift from long-term memory into working memory. Re-reading brings information into working memory, but it doesn’t exercise the lift, and improving the lift is what improves retention.)

The only time the spotter should help you lift the weight is when you can’t lift it despite trying your hardest.

And even then, the spotter should only give you just enough assistance to get you over the edge of lifting the weight. The spotter should be doing as little as possible while ensuring that you manage to eek out a successful rep.

In the same way, the only time you should look at reference material during review is if you can’t recall something after trying your hardest.

And while it’s okay to check reference material as a last resort, you should only peek once for a cue, and then try to recall the rest without looking again.

This weightlifting analogy generalizes beyond spaced repetition: in general, learning requires introducing “desirable difficulties” into the recall process, making it tough yet achievable.

But remember: just like little strength is built by attempting and failing to lift a too-heavy weight, little knowledge is built by attempting and failing a too-difficult learning task.

Even a desirable difficulty becomes undesirable if the learner is unable to overcome it.

Additionally, not all difficulties are desirable. Plenty of difficulties are undesirable even if they can be overcome.

For instance: sleep deprivation. Even if you overcome it, it’s not a productive challenge for building strength or knowledge.