An intriguing comment on Slashdot:

Why would I pay 8.00 for a paperback I know I'll probably only read once and then stick on a shelf or on a pile, when I can probably borrow the book for free from the Library? Psychology is fascinating...

Schopenhauer said it well: buying books would be great if we could also buy the time to read them. So, since we already know that we will never have that time then, maybe, we buy books to satisfy a certain sense of property. In other words, we get some sort of artificial brain sweetener. When I buy a book - I potentially know more.