[evanpw]

This is true of almost everything in math. You learn some definitions and techniques in one class, and it doesn't all become clear what's going on until you've used those to as the base layer for solving some other problems in the next class. Part of it is just that it's hard to teach you need the first concept in order to understand the second, but you need the second to understand why you should care about the first, so it's all a bit circular.