The constancy principle is central to Freud's theory of the human being as a biological organism which strives to maintain its excitation at a comfortable level. To achieve this goal involves avoiding external stimuli which are likely to prove excessive, and seeking those likely to be sufficient to affirm our awareness of being; internally, in the conscious and unconscious mind, we seek to discharge or block stimuli which threaten our equilibrium condition.
Freud's conception of this principle was developed during his collaboration with Josef Breuer (1892-5) and influenced by the work of Gustav Theodor Fechner (1801-87) – see “ The Pleasure Principle” �…
Editors. "Constancy Principle [Konstanzprinzip]". The Literary Encyclopedia. First published 22 October 2005
[http://www.litencyc.com/php/stopics.php?rec=true&UID=1609, accessed 21 February 2017.]