This article examines the signification of the principle of constancy as formulated in Freud's pre-psychoanalytical drafts and papers and, above all, in Entwurf. It is argued that Freud's principle differs significantly from seemingly similar principles proposed by Breuer and Fechner, and that it constitutes an assumption about the maintaining of a constant amount of kinetic energy whose primary purpose is not to return to a state of equilibrium, but, proceeding from the primary biophysical functions of discharge (principle of inertia) and accumulation (exigencies of life), to consolidate an asymmetry within the nervous system. This gives rise to a set of quasi-psychological dualisms: an energetic dualism between kinetic and tonic energy; a systemic dualism between the impermeable and permeable neurons; and a processual dualism between courses of the excitations with and without the inhibiting influence of the ego. Further, it is argued that the primary purpose of the principle of constancy is to make itself and its material preconditions redundant, i.e. to enable an “auto-subtraction”, facilitating its repression. Lastly, it is argued that the constitution of psychoanalysis is dependent on this repression, and that “Beyond the Pleasure Principle” may be understood as the return of the repressed principle of constancy.