I used to hang out at used bookstores regularly. Mostly to find cheap but good quality books for my kids when they were younger. I once managed to get a used copy of Paul Graham's On Lisp which was discarded from the technical library of a company somewhere.

The main point of interest is that physical items age and retain artifacts of their lives. I found a childrens book that was discarded from an American library where a girl had scrawled in pencil that she was proud that she finished it. I've seen one which was awarded to a man for being top of his class in college in the early 1900s. The bookshop I used to visit once had a book sold to him which contained a letter from Rabindrnath Tagore in the original in between the leaves of the book.

It's a fascinating feeling and quite primal.

I recently read a sci-fi book from the library. A previous borrower had jotted notes/corrections/criticisms of the author's science in the margins, in the tiniest, neatest handwriting I've ever seen. None of the "problems" they pointed out detracted from the story, but I guess they really wanted to show off their personal theories of FTL travel to whoever borrowed the book next. It was hilarious, and I'll remember the book forever because of that.