If I sell you something, we exchange items of value. You give me money, I give you stuff, or a service. The deal is done. We're even. Even steven, in fact.
That's fine, but it doesn't explain potlatch or the mystery of art or the power of a gift.
If I give you something, or way more than you paid for, an imbalance is created. That imbalance must be resolved.
Perhaps we resolve it, as the ancient Native Americans did, by acknowledging the power of the giver. In the Pacific Northwest a powerful chief would engage in potlatch, giving away everything he owned as a sign of his wealth and power. Since he had more to give away, and the power to get more, the gifts carried real power, and others had to accept his power in order to engage.
Or we resolve it by acknowledging the creativity and insight of the giver. Artists do this every time they put a painting in a museum or a song on the radio. We don't pay for the idea, but we acknowledge it. And then, if it's particularly powerful, it changes us enough that we become givers, contributing to someone else, passing it along.
Sometimes we resolve the imbalance by becoming closer to the brand or the provider. We like getting gifts, we like being close to people who have given us a gift and might do it again.
And sometimes, in the case of international aid, we resent the rich giver, the one with so much more power, and thus create a cycle of dependence that does neither side any good. This sort of gift isn't much of a gift at all.
When done properly, gifts work like nothing else. A gift gladly accepted changes everything. The imbalance creates motion, motion that pushes us to a new equilibrium, motion that creates connection.
The key is that the gift must be freely and gladly accepted. Sending someone a gift over the transom isn't a gift, it's marketing. Gifts have to be truly given, not given in anticipation of a repayment. True gifts are part of being in a community (willingly paying taxes for a school you will never again send your grown kids to) and part of being an artist (because the giving motivates you to do ever better work).
Plus, giving a gift feels good.