What is Reality principle?

In Freudian psychology and psychoanalysis, the reality principle is the ability of the mind to assess the reality of the external world, and to act upon it accordingly, as opposed to acting on the pleasure principle.

Allowing the individual to defer instant gratification, the reality principle is the governing principle of the actions taken by the ego, after its slow development from a "pleasure-ego" into a "reality-ego": it may be compared to the triumph of reason over passion, head over heart, rational over emotional mind, human values over animal instinct.