Whereas the contents of the personal unconscious are acquired during the individual’s lifetime, the contents of the collective
unconscious are invariably archetypes that were present from the beginning.
Their relation to the instincts has been discussed elsewhere.
The archetypes most clearly characterized from the empirical point of view are those which have the most frequent and the most disturbing influence on the ego.
These are the shadow, the anima, and the animus.
The most accessible of these, and the easiest to experience, is the shadow, for its nature can in large measure be inferred from the contents of the personal unconscious.
The only exceptions to this rule are those rather rare cases where the positive qualities of the personality are repressed, and the ego in consequence plays an essentially negative or unfavourable role.
The shadow is a moral problem that challenges the whole ego-personality, for no one can become conscious of the shadow without considerable moral effort.
To become conscious of it involves recognizing the dark aspects of the personality as present and real.
This act is the essential condition for any kind of self-knowledge, and it therefore, as a rule, meets with considerable resistance. Indeed, self-knowledge as a psychotherapeutic measure frequently requires much painstaking work extending over a long period. ~Carl Jung, CW 9ii, Para 13-14