Abstract: This essay challenges some widely held understandings about rationality and choice, and uses that challenge to develop some conclusions about the appropriate domain of law. In particular, it suggests that many well-known anomalies in individual behavior are best explained by reference to social norms and to the fact that people feel shame when they violate those norms. Hence, there is no simple contrast between "rationality" and social norms. Individual rationality is a function of social norms. It follows that social states are often more fragile than might be supposed, because they depend on social norms to which people may not have much allegiance. Norm entrepreneurs -- people interested in changing social norms -- can exploit this fact; if successful, they produce what norm bandwagons and norm cascades. Collective action might be necessary to solve some unusual collective action problems posed by existing norms. And for many purposes, it would be best to dispense with the idea of "preferences," despite the pervasiveness of that idea in positive social science and in arguments about the appropriate domains of law.