Actually, the part I found difficult about music theory, is that that there are tons of stuff you're supposed to remember.
They are not difficult to understand, and they are even easy to derive from some basic rules.
But you do have to remember them, not derive them at will, to be able to think musically and play fluently.
I think that's my problem with Chemistry too, as opposed to Physics. There was always tons of stuff to remember when studying chemistry, while just remembering a few basic rules and deriving everything else was possible in Physics (I talk about High School grade material, of course).
This is exactly why Math was Good for me in High School and History was Terrible. And the thing is, with an understanding of history a lot can be derived, or at least worked out, yet history class was all about memorizing names and dates and the relationships and flow of history was often something that felt coincidental to what was being taught.
Id say by the time you are playing fluently with these ideas you are no longer remembering them ... its further than that you body knows and executes them.
They are not difficult to understand, and they are even easy to derive from some basic rules.
But you do have to remember them, not derive them at will, to be able to think musically and play fluently.
I think that's my problem with Chemistry too, as opposed to Physics. There was always tons of stuff to remember when studying chemistry, while just remembering a few basic rules and deriving everything else was possible in Physics (I talk about High School grade material, of course).