"It turns out that the more we pay for something—and the payment can take the form of money, time or physical pain, as with the filling of a cavity—we’re more likely to believe that the product or service is effective, and thus worth the cost. It’s perverse but true: pain makes us loyal, and the surest way to improve the performance of a product is to raise its price. ... A painful surgery is like an expensive energy drink. We assume the intervention was effective because it would be too distressing to believe otherwise. Because if our dentist made a mistaken diagnosis then the pain was wasted: we endured the drill for no reason at all."