Walk into any fast-food restaurant, and you can watch a small crowd of ordinary people doing something that is utterly irrational: eating junky, excess-weight-inviting food likely to leave them feeling bad about their bodies and open to a host of serious ills. We literally line up to trade our health and self-image for a few minutes of pleasant mouth feel and belly comfort—because the latter is right here, right now, whereas the former is months, years and decades away.