The way I see it: You donate blood and you donate to a charity. You pay for music and you pay for books. When you donate you don't expect to get something back

The way I see it: You donate blood and you donate to a charity. You pay for music and you pay for books. When you donate you don't expect to get something back in return. When you pay you expect something back. Even though no one is forcing you to give in either case the mental model is a quite different. For example, as a musician I want people to pay me because they enjoy my music not because they feel that I need the money. As a listener I will pay someone if I enjoy their music - I don't really care about the financial status of the musician.