“There are endless variations on this sort of tit-for-tat, or almost tit-for-tat, gift exchange. The most familiar is the exchange of presents: I buy someone a beer; they buy me the next one. Perfect equivalence implies equality. But consider a slightly more complicated example: I take a friend out to a fancy restaurant for dinner; after a discreet interval, my friend does the same. As anthropologists have long been in the habit of pointing out, the very existence of such customs—especially, the feeling that one really ought to return the favor—can’t be explained by standard economic theory, which assumes that any human interaction is ultimately a business deal and that we are all self-interested individuals trying to get the most for ourselves for the least cost or least amount of effort.28 But this feeling is quite real, and it can cause genuine strain for those of limited means trying to keep up appearances. So: Why, if I took a free-market economic theorist out to an expensive dinner, would that economist feel somewhat diminished—uncomfortably in my debt—until he had been able to return the favor? Why, if he were feeling competitive with me, would he be inclined to take me to someplace even more expensive?”