Why do you buy a book?

I have a list of books to read. I usually add books to my list after reading someone reccomend the book online (for example, "Daniel Tammet's book Born on a Blue Day is also very good.")

Also, I never buy books if I can get them from a nearby library. And if I can't get the book from the library, I'll only buy it if I think it'll be really good. I've only bought myself two books in the last two or three years.