Man is not truly one but truly two... I learned to recognize the thorough and primitive duality of man; I saw that, of the two natures that contended in the field of my consciousness, even if I could rightly be said to be either, it was only because I was radically both... I had learned to dwell with pleasure, as a beloved daydream, on the thought of the separation of these elements. If each, I told myself, could be housed in separate identities, life would be relieved of all that was unbearable... It was the curse of mankind that these incongruous [entities] were thus bound together - that in the agonized womb of consciousness, these polar twins should be continuously struggling.

Robert Louis Stevenson, Dr. Jekyll and Mr. Hyde