We therefore emphatically affirm that in addition to the repressed material the unconscious contains all those psychic components that have fallen below the threshold, as well as subliminal sense-perceptions.  Moreover we know, from abundant experience as well as for theoretical reasons, that the unconscious also contains all the material that has not yet reached the threshold of consciousness.  These are the seeds of future conscious contents.  Equally we have reason to suppose that the unconscious is never quiescent in the sense of being inactive, but is ceaselessly engaged in grouping and regrouping its contents.  This activity should be thought of as completely autonomous only in pathological cases; normally it is co-ordinated with the conscious mind in a compensatory relationship.  2EoAP 127

(A) so-called normal person would probably be able to break (an) emotional bond in one or the other direction by a powerful act of will, or else – and this is perhaps the more usual thing – he would come through the difficulty unconsciously, on the smooth path of instinct, without ever being aware of the sort of conflict that lay behind his headaches or other physical discomforts.  But any weakness of instinct (which may have many causes) is enough to hinder a smooth unconscious transition.  Then all progress is delayed by conflict, and the resulting stasis of life is equivalent to a neurosis.  In consequence of the standstill, psychic energy flows off in every conceivable direction, apparently quite uselessly. 

For instance, there are excessive innervations of the sympathetic system, which lead to nervous disorders of the stomach and intestines; …. Or fantasies and memories, uninteresting enough in themselves, become overvalued and prey on the conscious mind (mountains out of molehills). 

In this state a new motive is needed to put an end to the morbid suspension.  Nature herself paves the way for this, unconsciously and indirectly, through the phenomenon of the transference (Freud).