Here's this weeks BTT. My answers will be brief because I'm stealing a little time from vacation to blog.
Do you have multiple copies of any of your books? I don't tend to keep many books (wow, that's probably an admission here). I have a few favorites on a bookshelf (and no duplicates that I know of). I tend to loan books out and don't worry about getting them back. I also donate good hard cover copies to my local library. They get put in the collection for other people to read. I have, accidentally, borrowed the same book more than once either from a library or a friend. It seems to happen if the cover is different. Once I start reading, I realize and return it.
If so, why? Absent-mindedness? You love them that much? First Editions for the shelf, but paperbacks to read? The only duplicates I have are borrowed, and it truly is absent-mindedness, especially if the cover is different. I seem to have a memory for covers.
If not, why not? Not enough space? Not enough money? Too sensible to do something so foolish? Space is one of the issues, for sure. I don't think it's foolish to keep a personal library. In fact, my classroom library has 100s of books, and I add to it all the time. That's probably why I can give away books at home.