Surely you've read through a book and thought, "I wish I could find where I saw that!" Sometimes you may like the books' explanation over whatever you find online.
I found the index and table of contents are not always helpful when you want to use a paperback to reference from. I find it beneficial to write in your own index in any blank page provided by your book! Don't worry, you don't need to sell it anyhow. You can do this for any book, of course. Manga?
We used to not have the internet and relied on these things.
Bonus I have tried making flashcards. I have 400+ from this very book. I have never really studied them. I tried... I think books shine as references. No need to dwell on them with needless re-study. Find something else and don't look back.