When I studied Physics, I could sometimes take hours to digest a single page of a textbook or my lecture notes - providing that it was a good textbook. It’s not enough to just understand what is written. You have to understand why it is like described. Why it can’t be different - or could it? You need to build an intuition for both the physics and the math describing it. You have to push until it clicks. It’s hard wo…
math requires something different than memory, it requires understanding and fluency in its variety of symbolic languages, which can only built with intellectually engaged work.
of course these are rarely static (after all one can learn proofs of theorems without being able to solve any problem), hence the need for the "muscle memory" of how to apply these techniques to the particular patterns.