lambda calculus
Last night around 3am Eli decided to teach me about lambda calculus. He said it would take 5 minutes. It didn't. Although I find that I still remember enough of LISP for it to make a little bit of sense to me. I guess I wish I caught on to things like that a lot faster.

no subject
I had the same problem when we started to learn algebra in elementary school. My brain immediately went "Oh! Like BASIC!" and refused to cope with algebra in the abstract. Building a second mental map that was 90% similar to the first was harder than starting from scratch.
I wonder if learning a few new languages that implement lambda calc. differently would help.