[goerz]

I find that with anything where I feel I have to "start over" every time I try to get back into it, the solution is to consciously memorize the key points and the notation of anything I'm learning, using (Anki) flashcards. Michael Nielsen recently wrote a great overview of the process recently: http://augmentingcognition.com/ltm.html

Making sure the basics stick in long-term memory, you can then build on that anytime in the future without having to review everything.