Freud's psychoanalytic theories
According to Freud, the id is the part of the unconscious that seeks pleasure. His idea of the id explains why people act out in certain ways, when it is not in line with the ego or superego.  The id is the part of the mind which holds all of humans' most basic and primal instincts.  It is the impulsive, unconscious part of the mind that is based on desire to seek immediate satisfaction.  The id does not have a grasp on any form of reality or consequence.  Freud explains that the pleasure principle is controlled by the id because it makes people engage in need-satisfying behavior without any accordance to what is right or wrong.  Freud compares the id and the ego to a horse and a rider.  The id is compared to the horse, which is directed and controlled by the ego (the rider).  This example goes to show that although the id is supposed to be controlled by the ego, they often interact with one another according to the drives of the id.