Spaced repetition memory systems are extremely efficient, but that phrase doesn’t get across the nature of the efficiency. There are lots of things you might try to improve yourself—reading more books, talking to experts, etc. These things will all help, of course, but they also yield diminishing returns fairly rapidly. Spaced repetition doesn’t work like this. If you spend a few extra minutes reviewing prompts about something you’ve read, you’ll get vastly more out of the material. From that point, achieving essentially permanent recall requires only marginally more effort.
Matuschak, A., & Nielsen, M. (2019, October 0). How can we develop transformative tools for thought? https://numinous.productions/ttft
Given that the essay takes about 4 or so hours to read, this suggests that a less than 50% overhead in time commitment can provide many months or years of retention for almost all the important details in the essay.
This is the big, counterintuitive advantage of spaced repetition: you get exponential returns for increased effort. On average, every extra minute of effort spent in review provides more and more benefit. This is in sharp contrast with most experiences in life, where we run into diminishing returns. For instance, ordinarily if you increase the amount of time you spend reading by 50%, you expect to get no more than 50% extra out of it, and possibly much less. But with the mnemonic medium when you increase the amount of time you spend reading by 50%, you may get 10x as much out of it. Of course, we don’t quite mean those numbers literally. But it does convey the key idea of getting a strongly non-linear return. It’s a change in the quality of the medium.