Feynman Notes

Every page in this book asks the same four things, in the same order: name the concept, explain it as if to somebody who has never heard of it, mark the exact point where that explanation ran out of words, then try again, shorter. The third box is the one that does the work. It is easy to reread a chapter fluently and mistake the fluency for understanding; it is much harder to write a plain explanation of the same chapter and notice exactly where it stops.

One hundred twenty pages hold that shape. A further run of plain ruled pages sits behind them for whatever does not fit inside four boxes: a diagram, a worked example, a question for someone who actually knows.

It does not grade the explanation. It does not know the subject either. It only keeps asking until the third box runs out of room, and what goes in that gap is the reader's problem, not the page's.