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 once experienced a tremendous moment
when you would have answered him:

“You are a god and never have I heard anything more divine!”

If this thought gained possession of you, it would change you as you are
or perhaps crush you; the question in each and every thing, “Do you desire
this once more, and innumerable times more?” would lie upon your actions
as the greatest weight! Or how well disposed would you have to become to
yourself and to life to crave nothing more fervently than this ultimate
eternal confirmation and seal?

Friedrich Nietzsche, The Gay Science