A psychoanalytic concept, originally proposed by Sigmund Freud, that compels people to defer gratification when necessary due to the obstacles of reality. The reality principle is governed by the ego, which controls the instant-gratification mentality of the id.
The reality principle is the exact opposite of the pleasure principle (which seeks immediate gratification). One is looked upon as more mature when they are acting in accordance with reality. As children we seek pleasure and try to avoid things that cause us suffering or pain, however as we get older we realize that there are certain situations where it is better to endure the suffering/pain than to be out of control or inappropriate.
Example: A person with a high sex drive must learn to control his or her impulses; it would be impractical and/or socially unacceptable to have sex every time he or she felt like it.
Fournier, G. (2010). Reality Principle. Psych Central. Retrieved on April 19, 2015, from http://psychcentral.com/encyclopedia/2009/reality-principle/