We must reckon with the possibility that something in the nature of the sexual instinct itself is unfavorable to the realization of complete satisfaction.
Sigmund FreudThe pleasure principle long persists, however, as the method of working employed by the sexual instincts, which are so hard to 'educate', and, starting from those instincts, or in the ego itself, it often succeeds in overcoming the reality principle, to the detriment of the organism as a whole.
Sigmund Freud