Can what you believe about a drink change how fast you run? Thirty runners complete a timed race. They are split into three equal groups based on their first-race times. Before a second race, each group drinks the same sweetened water. One group is told it boosts stamina. Another is told it has no effect. The third is told it will slow them down. You compare the second-race times across all three groups. Runners who believed the drink helped them ran faster. Those told it would hurt their performance ran slower.