In contrast to the subjectivism of the conscious mind the unconscious is objective, manifesting itself mainly in the form of contrary feelings, fantasies, emotions, impulses, and dreams, none of which one makes oneself but which come upon one objectively.
Source - C.G. Jung, The Undiscovered Self (Present and Future). CW 10: Civilization in Transition, par. 562.
The activity of consciousness is selective. Selection demands 'direction.' But direction requires the 'exclusion of everything irrelevant.' This is bound to make the conscious orientation one-sided. The contents that are excluded and inhibited by the chosen direction sink into the unconscious, where they form a counterweight to the conscious orientation. The strengthening of this counterposition keeps pace with the increase of conscious one-sidedness until finally a noticeable tension is produced. This tension inhibits the activity of consciousness to a certain extent, and though at first the inhibition can be broken down by increased conscious effort, in the end the tension becomes so acute that the repressed unconscious contents break through in the form of dreams and spontaneous images.
The more one-sided the conscious attitude, the more antagonistic are the contents arising from the unconscious, so that we may speak of a real opposition between the two. In this case the compensation appears in the form of a counter-function, but this case is extreme.
As a rule, the unconscious compensation does not run counter to consciousness, but is rather a balancing or supplementing of the conscious orientation. In dreams, for instance, the unconscious supplies all those contents that are constellated by the conscious situation but are inhibited by conscious selection, although a knowledge of them would be indispensable for complete adaptation. Normally, compensation is an unconscious process, i.e., an unconscious regulation of conscious activity. In neurosis the unconscious appears in such stark contrast to the conscious state that compensation is disturbed. The aim of analytical therapy, therefore, is a realization of unconscious contents in order that compensation may be re-established.
Source - C.G. Jung, Definitions (Compensation). CW 6: Psychological Types, pars. 694-695.
Art: Antonella Masetti Lucarella