the inferior function remains conscious, at least in its effects; but in a neurosis it sinks wholly or in part into the unconscious. For, to the degree that the greater share of libido is taken up by the favoured function, the inferior function undergoes a regressive development
Jung establishes the foundational mechanics of functional hierarchy: energic investment in the superior function causes the inferior to regress toward archaic, unconscious operation, with pathological implications in neurosis.
, Psychological Types, 1921thesis