The Psyche is the world's pivot; not only is it the one great condition for the existence of a world at all, it is also an intervention in the existing natural order and no one can say with certainty where this intervention will finally end … With all the more urgency, then we must emphasise that the smallest alteration in the psychic factor, if it be an alteration of principle, is one of the utmost significance as regards our knowledge of the world and the picture we make it.