For example, as a child, you wanted to learn things, so you did labor such as figuring out how to read, and you were paid in knowledge. Another example: as an adult, you have probably tried to think of something comforting to say to someone grieving a loved one's death, for no pay at all. I posit that if you had to live in a world where, starting tomorrow, you will never see a child learn anything, and nobody will care how you feel if your loved ones die; you would prefer going without everything you've ever paid money for.