[hyperpallium]

  You don't understand mathematics,
  you just get used to it - jvn

I used to want to understand math (intuition); now I think of it as learning a language: lots of vocab and rules with some pattern. You need to become fluent - practiced, like a cellist or cricketer.

It's also a language when someone is teaching it.

Prior knowledge is assumed; so it's difficult to detect that it is a gap that's making it difficult. When I finally realized my hard-won breakthroughs were about prior material, I dropped back to do that prior level... again and again.

This thorough approach is far too time-consuming for your needs. I really hope you find a quicker way - and please tell me!