My brain tends to retain information that it can "see" being played out or performed. Formulas and equations for example from math textbooks or whatever have to be focused on and drawn out as if I have a tiny go pro looking down the end of my pencil at what's being written in my mind as I read the content. Sounds strange but when I actively make myself retain it this way I can usually bring it back from my memory very well remembering the "go pro on pencil video" of the content I need to remember.