This study combines the psychology of bias and the economics of equilibrium. We focus on two of the most discussed perceptual biases found by psychologists who studied the role social norms in ethical decision making. First, psychologists found a general tendency of people to over-estimate how many other people engage in unethical behavior. We show that this bias causes more people to violate the norm than if the bias were corrected. Second, psychologists found a general tendency of a person to over-estimate how many other people act the same as he does. We show that this bias does not change the number of people who violate the norm, contrary to the predictions of some psychologists. When a person suffers from both biases, they can augment or undermine each other. In either case, we show that supplying accurate information will cause more people to conform to the norm. In general, we show that applying the equilibrium concept to psychological studies improves public policy recommendations by increasing precision in predicting aggregate behavior over time.