A ship is safe in harbor, but that's not what ships are for.
What if a demon crept after you into your loneliest loneliness some day or night, and said to you: “This life, as you live it at present, and have lived it, you must live it once more, and also innumerable times; and there will be nothing new in it, but every pain and every joy and every thought and every sigh, and all the unspeakably small and great in thy life must come to you again, and all in the same series and sequence – and similarly this spider and this moonlight among the trees, and similarly this moment, and I myself. The eternal sand-glass of existence will ever be turned once more, and you with it, you speck of dust!” – Would you not throw yourself down and gnash your teeth, and curse the demon that so spoke? Or have you once experienced a tremendous moment in which you would answer him: “You are a God, and never did I hear anything so divine!” If that thought acquired power over you as you are, it would transform you, and perhaps crush you; the question with regard to all and everything: “Do you want this once more, and also for innumerable times?” would lie as the heaviest burden upon your activity! Or, how would you have to become favourably inclined to yourself and to life, so as to long for nothing more ardently than for this last eternal sanctioning and sealing?