The fascinating thing about standard economic stories is exactly that: they assume that everybody wants that kind of closure. That all human relations are forms of exchange, because if everything is an exchange then it's true that we're both equals. We walk up, I give you something, you give me something, and we walk away. Or I give you something, you don't give me something right now, and you owe me. So if we have any ongoing relationships at all, it's because somebody is in debt.