You have the actual skills, when it comes to grammar. I have more of a intuitive feel for it. I couldn’t explain why it seemed wrong, but I knew it made my eyes pinwheel in their sockets. :)
Grammar and tax accounting are similar skills. Both involve categorizing objects and, literally or figuratively, performing computations upon them.
I might have been good at actual maths, too, if I made a real effort. Patrick the Other Son has been watching a lecture series on mathematical problem-solving, and I sometimes surprise him by coming up with a correct answer or at least a correct approach.