I work on the assumption that the half-life of knowledge gained from books, essays, and articles is about 2.5 years (I'm forgetful, but probably not more than a

I work on the assumption that the half-life of knowledge gained from books, essays, and articles is about 2.5 years (I'm forgetful, but probably not more than average). So I use a mechanical pencil to write small notes in the margins of books/essays. Then I write them up in a google doc (or if it's a coding book, on GitHub, usually in a public repo). My notes are always available and ~20-50x faster than if I were to re-read the book (and probably yield 90% of the value). An unexpected bonus is the perspective gained from scanning notes I took years ago. It teaches me a lot about the person I was at that point in time, and my ideas then usually differ from how I think about things now. Very valuable for introspection and perspective!