The psychologist Helmut Schulze has drawn attention to the remarkable fact that the word Freude ("joy") does not occur in Freud, who recognizes pleasure, but not joy. Schulze says, in substance, that when, sweating and exhausted, with sore fingers and aching limbs, we reach the summit of a difficult mountain, knowing that the even more difficult and dangerous descent lies ahead of us, this is not pleasure but one of the greatest joys on earth. Pleasure may be achieved without paying the price of strenuous effort, but joy cannot. Intolerance of unpleasurable experience converts the natural ups and downs of human life into an artificial plain, the great wave of mountain and valley becoming a scarcely noticeable ripple, and light and shade a monotonous gray. In short, intolerance of unpleasurable experience creates deadly boredom.