Feynman is a physicist who owns a theory that if someone really understands a topic, he should be able to explain it to a kid who has zero knowledge in this field.
If you can't explain a topic very well, you need to go home and sit down to look after the things you are missing.
So every time you want to learn something, try to pretend to teach it to a kid.
Trunk Based Knowledge
When you want to learn something, you may want to learn one first, then another. But that's not a very smart way of learning.
Andrei recommends that when you want to learn a thing, you always need to start from the basic. For example, if you want to learn to play the violin, you should understand the chores. Otherwise, your learning process will be very miserable.
Therefore, anytime you want to learn something, start from the root, and then learn the leaves. Because the leaves will change, but the root will always stay, or lasts as long as possible.