How, if some day or night, a demon were to sneak after you into your 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 sign . . . must return to you—all in the same succession and sequence—even this spider and this moonlight between the trees, even this moment and I myself. The eternal hourglass of existence is turned over and over—a grain of dust!" Would you not throw yourself down and gnash your teeth and curse the demon who spoke thus? Or have you once experienced a tremendous moment when you would have answered him: "You are a god and never did I hear anything more godlike!" If this thought were to gain possession of you, it would change you as you are, or perhaps crush you. The question in each and everything, "Do you want this more and innumerable times more?" would weigh upon your actions as the greatest stress. Or how well disposed would you have to become to yourself and to life to crave nothing more fervently than this ultimate eternal confirmation?
Friedrich Nietzsche, Gay Science