You write that we are "pawns in a game whose forces we largely fail to comprehend." What are some of those forces?We're all like Jekyll and Hyde, and we all underpredict the effect of emotion and passion. Think of road rage, or couples who fight and say awful things. When we're in the cold state, we don't understand the hot state. If you think about it from an evolutionary perspective, emotions were designed to eliminate thinking. You're in the jungle. You see a tiger. You don't want to stand there thinking, Should I run? You want emotion to take over and execute a plan of action.

Many of your experiments (see "Testing the Theory," below) reveal how cues from the environment affect our decisions. What lessons do you draw from that?We should alter our environment to improve our behavior, rather than relying on just "being reasonable." Consider reckless teen drivers, for instance. Cars could be designed so that the parents get a phone call if the teen drives fast or wild. Or, we could have a self-control credit card that limits purchases on clothing or eating out. You would design penalties for exceeding the limits. Maybe your spouse or a neighbor would be notified, or a donation would be sent to some designated group.

Testing the TheoryTo demonstrate the tricks our minds play on us, Ariely conducted a few fascinating experiments. Behold the results.