For everyone whose guiding principle is adaptation to external reality, imagination is something reprehensible and useless. And yet we know that every good idea and all creative work are the offspring of the imagination, and have their source in what one is pleased to call infantile fantasy. Not the artist alone, but every creative individual whatsoever owes all that is greatest in his life to fantasy. The dynamic principle of fantasy is play, a characteristic also of the child, and as such it appears inconsistent with the principle of serious work. But without this playing with fantasy no creative work has ever yet come to birth. The debt we owe to the play of imagination is incalculable. It is therefore short-sighted to treat fantasy, on account of its risky or unacceptable nature, as a thing of little worth. It must not be forgotten that it is just in the imagination that a man's highest value may lie. I say 'may' advisedly, because on the other hand fantasies are also valueless, since in the form of raw material they possess no realizable worth. In order to unearth the treasures they contain they must be developed a stage further. But this development is not achieved by a simple analysis of the fantasy material; a synthesis is also needed by means of a constructive method.

Psychological Types by Carl Gustav Jung