Winston Graham said this quote
“ Yet, although he could not quite work this out in simple terms in his own mind, the very savour of life, he thought, was itself enhanced if it were not totally taken for granted. Perhaps it was something to do with the whole philosophy of the world into which we were born. If we lived for ever, who would look forward eagerly to tomorrow? If there were no darkness, should we appreciate the sun? Warmth after cold, food after hunger, drink after thirst, sexual love after the absence of sexual love, the fatherly greeting after being away, the comfort and dryness of home after a ride in the rain, the warmth and peace and security of one’s fireside after being among enemies. Unless there was contrast there might be satiety. ”