The eternal recurrence is most heavily referred to by Friedrich Nietzsche in his 1883 Thus Spoke Zarathustra, where it serves primarily as a thought experiment proposed by the title character (Zarathustra) that is meant to designate a supreme achievement of human development; the ascension to a higher type of consciousness in man.
In Zarathustra, Nietzsche conceives of a cyclical universe, where every event is ever recurring, across an infinite stretch of time, forever. Nietzsche’s intent is to focus the mind of his readers on a possible reality in which every action they had committed (all faults, setbacks, mistakes, and wrongdoings) was bound to be repeated by them, an infinite amount of time. Where they would be forced to endure their shame and grief over and over again, unable to change or improve on any past misdeeds, for all eternity. And then to ask the question: “Would you be willing to bear such a reality?” Would a person be able to cope with knowing that s/he will have to helplessly live through all the pains, heartbreaks, bad decisions, and grief that s/he has already struggled through once in life? And would this person, aware of this eternal recurrent, still manage to affirm a will to live?
Nietzsche believed that most people alive would decisively shriek a unanimous “No!” to such a proposition, because it would seem too bleak and fatalistic a fate to have to eternally return to one’s life’s errors, infinitely doomed to recommit one’s sins (for lack of a better term). Nietzsche saw this as a reflection of the destitute modern man has surrendered himself to; the wanting denial of one’s true existence. He contrasted this with what he called amor fati (Lat. love of fate):
My formula for greatness in a human being is amor fati: that one wants nothing to be different, not forward, not backward, not in all eternity. Not merely bear what is necessary, still less conceal it—all idealism is mendaciousness in the face of what is necessary—but love it (Ecce Homo, “Why I am So Clever,” section 10).
To be able to look at the compilation of one’s life, with all one’s mistakes and regrets, and still unashamedly proclaim one’s desire to relive it all as is (with no intent to alter one’s past actions), is according to Nietzsche the ultimate affirmation of life—a full embrace of one’s existence, a testament to the arrival of the overman (Ger. Übermensch).
Although the eternal recurrence was a central theme in Thus Spoke Zarathustra, Nietzsche seemed to have somewhat abandoned the thought experiment in much of his later work (he makes no mention of it in either Beyond Good and Evil or On the Genealogy of Morals). However, this appears to be a hasty conclusion, since Nietzsche does make continuous references to the basic sentiment found in his 1883 philosophical novel, and seems to be expanding on the same core concepts in his later writings.
This eternal return, and its importance in signifying the coming of the overman, is Nietzsche’s attempt to offer a possible redemption narrative for humanity. A means by which man can take the fatalistic nature of life, and surpass its dire implications by ascending beyond them into a realm of complete oneness with all the facts and events that come together to compose one’s life story. Yet, this redemption is not inevitable, for man (or “modern man,” as Nietzsche would say) is in a constant state of rejecting amor fati, and moving away from self-acceptance, in favor of finding acceptance with “higher” ideals, that are imagined to dwell exterior and superior to oneself. This is the fate of what Zarathustra called the “last man”—the alternate fate of mankind—the final descend of mankind to a sheepish, complacent shell of what he once was, living in fear of his own existence.