I just take handwritten notes, then convert them into carefully designed and tagged cards in Anki. Even if I forget something, searching my Anki deck will usually not just tell me the information, but what book it came from, and often which page. I'm pretty diligent about careful note collation. I've definitely gotten better since I read "The Organized Mind", a book which was so enlightening for my persona that I built more than 1000 cards to remember as many of its concepts as I could.

Regardless, I'm reading my previous comment and should admit that I'm quite intense about efficiency in learning. Less so about money. I've spent a lot of time tutoring, making this an important subject to me and I get.... emotional. I apologize if my original comment seems rude. It certainly feels that way to me.