No. Carry a notebook. Long after you’ve given the book away, you’ll always have your notes.

why not both? mark up the book while you're reading, reflect in your notebook on what you read

Exactly. Personally, I gravitate toward book and topic-specific notes and highlights in the book itself and use the notebook for bigger-picture things for which book references play some role. I do a lot of highlighting in ebooks and lately I've started using LogSeq. I'll pull quotes from books into LogSeq and then tag them with whatever #bigger-picture topic I deem relevant, mimicking what I do on paper.

The notes only make sense with context. I'm not interested in copying three or so sentences for every small comment or even just a highlight.

Do you have tips to start using notebooks instead of marking books? I personally like to underline stuff in my books, when I start a new novel it's often people, places and events. I'm not sure what would be the notebook equivalent of that. Writing down what I would underline? It seems tedious and you loose context and the sense of proximity between words.

For my textbooks, I use little record cards. I write the book reference on the top line, then whatever notes or quotations etc. If it's a heavily referred to book, I sometimes use different colour cards to mean different things.

When I return the book to the library etc., I take all my record cards out and put them in a little perspex index box.

Sometimes I use the record cards to then start some more detailed notes in a notebook; sometimes the record cards refer to a page in my notebooks where I've attempted a derivation etc.

Who said anything about throwing the book away?