Self-explanation and the Feynman technique
Explaining to yourself why each step is true, in plain words, is one of the fastest ways to find what you don't really understand.
The evidence
In Chi, Bassok, Lewis, Reimann & Glaser (1989), Self-Explanations, Cognitive Science 13, 145–182, students studied worked physics examples. The students who learned most generated many more explanations to themselves while studying: why a step follows, what a term means, where it fits.
Dunlosky, Rawson, Marsh, Nathan & Willingham (2013), Improving Students' Learning With Effective Learning Techniques, Psychological Science in the Public Interest 14, 4–58 rated self-explanation and "elaborative interrogation" (asking why a fact is true) as moderately useful.
The "Feynman technique"
The popular version: explain the idea simply, as if to a newcomer; notice where you get vague or stuck; go back to the source for exactly that; explain again. It is named after the physicist Richard Feynman, who was famous for explaining clearly, but it isn't a method he wrote down. It's a practical form of self-explanation.
How to do it
- Explain out loud or in writing, without looking.
- Ask "why is this true?" and "when would it fail?" for each step.
- Mark every place you hand-wave. Those are your gaps, and the next thing to study.