Freud would say that the "superego" portion of the mind tells a person...
The superego is the moral part of the identity and gives the ethical models by which the ego works. The superego's reactions, denials, and hindrances frame a man's conscience and its positive yearnings and beliefs speak to one's idealized self-image. The superego's capacity is to control the id's driving forces, particularly those which society precludes, for example, sex and hostility etc.