The Feynman Technique
As for testing whether we really understand something after we’ve read it, there is a powerful and elegant technique called the Feynman Technique.
Step 1. Choose the topic or concept that you are trying to understand. Take a blank piece of paper and write the name of the topic at the top.
Step 2. Assume you’re teaching the topic to someone else. Write out a clear explanation of the topic, as if you were trying to teach it. A great way to learn is to teach. You identify gaps in your knowledge very quickly when trying to explain something to someone else in simple terms.
Step 3. If you get bogged down, go back to the source materials. Keep going back until you can explain the concept in its most basic form.
Step 4. Go back and simplify your language. The goal is to use your own words, not the words of the source material. Overly elaborate language is often a sure sign that you don’t fully understand the concept. Use simple language and build on that with a clear analogy. An example that springs to mind is Warren Buffet’s explanation of compound interest (i.e., interest earned on interest), when he likened it to a snowball that gathers snow as it rolls down a hill