I don't buy books. I like to read, but I never finish a book before I get bored of it, so I don't buy books.

I would gladly pay for half a book after I'm done reading the half that i read, but stores don't sell me half a book, for half the price.

So instead, I borrow the book from my friend, read half of it, and then return it. The store doesn't get any income from me at all.