Enantiodromia. Literally, "running counter to," referring to the emergence of the unconscious opposite in the course of time.
This characteristic phenomenon practically always occurs when an extreme, one-sided tendency dominates conscious life; in time an equally powerful counterposition is built up, which first inhibits the conscious performance and subsequently breaks through the conscious control. ["Definitions," Ibid, par. 709.]
Enantiodromia is typically experienced in conjunction with symptoms associated with acute neurosis, and often foreshadows a rebirth of the personality.
The grand plan on which the unconscious life of the psyche is constructed is so inaccessible to our understanding that we can never know what evil may not be necessary in order to produce good by enantiodromia, and what good may very possibly lead to evil.[The Phenomenology of the Spirit in Fairytales," CW 9i, par. 397.]