I’ve never gotten rid of a book. All the books I’ve bought since I was 13 at a bookstore in my junior high I still have. Tattered copies of James Bond novels, Ray Bradbury paperbacks with a cover price of 75 cents. I’ve never sold books to a second-hand store.
I’ve sold some game books, like RPG modules. I sold my copy of the original Deities & Demigods (with the Cthulhu references) at Gen Con and it paid for my hotel room that weekend. Same thing with my original D&D books in the little brown box.
I don’t have as many books as some folks I know. They’d need another apartment just to store them all. But for me, I’ve still got ’em. All of them.