How does the next paragraph end?

How to retain knowledge
Use spaced repetition.
If you want to remember something, don't repeat it over and over to yourself-this is known as massed repetition. Instead, let some time elapse before you repeat it.
Ideally, you want to try to retrieve the information exactly at the moment when you were about to forget it. The difficulty of retrieving the information correlates to how strongly you will remember it.