I feel the same way whenever I think about quantum mechanics, fluid dynamics, thermodynamics, medical terminology, probability/statistics, functional programming, APL, and internal combustion engine repair manuals. For me, the biggest barrier to grokking something is almost always terminology.

I'm not sure if not knowing is better or worse than forgetting. I used to really excel at multivariable calculus and now I have to ask people on physics forums or wolfram alpha to solve basic integrations. I really, really wish they made Cliffs Notes for people who already learned something. For example I think every college course should have on the order of a one hour review video that covers everything. Maybe a hybrid of spaced interval learning and Khan Academy.