According to most economists we humans really are extremely rational creatures—hyperrational really, since when we make errors in judgement, such as failing to save enough for retirement, we’re really saving enough to satisfy our expected utility. But as the Economist succintly put it, “Economists make sense of the world by assuming that people know what they want. Advertisers assume that they do not. Who is right?” Good question. And the answer is: the advertisers.