When faced with their own aggression and destruction, humans often internalize the instinct—or send it “back where it came from, i.e., directed against the ego” (65). The result is “conscience,” which “exercises the same propensity to harsh aggressiveness against the ego that the ego would have liked to enjoy against others” (65). Conscience manifests as a “sense of guilt” and “the need for punishment” (66). This is a chief function of the super-ego, the part of the mind that, on behalf of society, watches over the ego "like a garrison in a conquered city” (66).

Society wants individual egos to recognize certain thoughts and actions as evil. Not every such act will be bad for a given ego: “[O]n the contrary, it can also be something that it desires, that would give it pleasure” (66). A person learns to avoid certain behaviors for a simple reason: “If he loses the love of others on whom he is dependent, he will forfeit also their protection against many dangers” (66) and may also be subject to punishment. Even thinking of doing something bad gives rise to pangs of conscience, as intent can also be cause for rejection and punishment.