"Why don't I get this?" is a statement commonly made by many students. It's steeped in frustration, anxiety, and anger. Or "Oh, I knew that!" after the principle is revealed to be something they did learn but couldn't apply well. This is why understanding the basic principles and then working your way up to the more difficult concepts is so important. Instead of absorbing information 'like a sponge,' or passive learning, doing something- relating something... engaging with the material by asking questions and making memorable connections in your brain is immensely more powerful AND useful.
A simple example:
If I knew x(a + b) = xa + xb, then I can infer that x(1/2 + b/y) = x/2 +xb/y.
If I knew x(a + b), then what about x(a + b + c)? It must be xa + xb + xc!
Logic builds on logic and wondering about the next logical conclusion budges your brain to think beyond the box.