In a period of human history when all available energy is spent in the investigation of nature, very little attention is paid to the essence of man, which is his psyche, although many researches are made into its conscious functions. But the really complex and unfamiliar part of the mind, from which symbols are produced, is still virtually unexplored. It seems almost incredible that though we receive signals from it every night, deciphering these communications seems too tedious for any but a very few people to be bothered with it. Man’s greatest instrument, his psyche, is little thought of, and it is often directly mistrusted and despised. “It’s only psychological” too often means: It is nothing.
C. G. Jung - Man and His Symbols (1964)