Governed by the id, it refers to the gratification of needs and the avoidance (or discharge) of unpleasurable tensions by means of, for example, hallucinations and fantasy. Originally, introduced by Sigmund Freud (1856-1939) as the unpleasure principle from the German word Lustprinzip, it is associated with a primitive id function in infant development during which there is an inability to distinguish reality from fantasy.
See Anhedonia, Ego, Hedonism, Hydraulics, Id, Psychoanalysis, Reality principle, Superego