What, if some day or night a demon were to steal after you in your loneliest loneliness and say to you: “This life as you now live it and have lived it, you will have to live once more and innumerable times more; and there will be nothing new in it, but every pain and every joy and every thought and sigh and everything unutterably small or great in your life will have to return to you, all in the same succession and sequence — even this spider and this moonlight between the trees, and even this moment and I myself. The eternal hourglass of existence is turned upside down again and again — and you with it, speck of dust!” — Would you not throw yourself down and gnash your teeth and curse the demon who spoke thus? Or have you experienced a a tremendous moment in which you would have answered him, “You are a God and never have I heard anything more divine!” If this thought gained power over you it would, as you are now, transform and perhaps crush you, the question in all and everything: “do you want this again and again, times without number?” would lie as the heaviest burden upon all your actions. Or how well would you have to be disposed towards yourself and towards life would you have to become to have no greater desire than this eternal sanction and seal?
Nietzsche, The Gay Science, translated by R.J. Hollingdale