Morality is a set of rules that enable people to live together in harmony, and virtue involves internalizing those rules. Insofar as virtue depends on overcoming selfish or antisocial impulses for the sake of what is best for the group or collective, self-control can be said to be the master virtue. We analyze vice, sin, and virtue from the perspective of self-control theory. Recent research findings indicate that self-control involves expenditure of some limited resource and suggest the analogy of a moral muscle as an appropriate way to conceptualize virtue in personality. Guilt fosters virtuous self-control by elevating interpersonal obligations over personal, selfish interests. Several features of modern Western society make virtue and self-control especially difficult to achieve.