Memorize for the grade and it’s gone by summer. Understand it and it’s yours for life.

Facts held for a test are stored in a way designed to be released, and they do exactly that. Understanding attaches to things you already know, which is why it stays; it has somewhere to live. The two feel similar the night before and are completely different six months later.

After studying something, close the book and explain it to an empty room in your own words. Wherever you stumble is the part you memorised, and that is the part worth going back to.