Eternal Return dictates that all things in existence recur over and over again for all eternity. This is to say that human history is a preset circle without progress, the same events arising perpetually and doomed never to alter or to improve. Existence is thus weighty because it stands fixed in an infinite cycle. This weightiness is “the heaviest of burdens”, for “if every second of our lives recurs an infinite number of times, we are nailed to eternity as Jesus Christ was nailed to the cross.” At the same time, it is necessary for any event to occur in the cycle of events exactly as it has always occurred for the cycle to be identical; consequently, everything takes on an eternally fixed meaning. This fact prevents one from believing things to be fleeting and worthless.
The inverse of this concept is Kundera’s “unbearable lightness of being.” Assuming that eternal return were impossible, humankind would experience an “absolute absence of burden,” and this would “[cause] man to be lighter than air” in his lack of weight of meaning. Something which does not forever recur has its brief existence, and, once it is complete, the universe goes on existing, utterly indifferent to the completed phenomenon. “Life which disappears once and for all, which does not return” writes Kundera, is “without weight…and whether it was horrible, beautiful, or sublime…means nothing.” Each life is insignificant; every decision does not matter. Since decisions do not matter, they are “light”: they do not tie us down. However, at the same time, the insignificance of our decisions – our lives, or being – is unbearable. Hence, “the unbearable lightness of being.” On the other hand, eternal existence would demand of us strict adherence to pre-scripted rules and laws; a sense of duty and rigorous morality.
“What then shall we choose? Weight or lightness?” Kundera notes that this is not a new question. Parmenides posed it in the sixth century BC. He saw the world divided into pairs of opposites: light/darkness, fineness/coarseness etc. One half of the opposition he called positive (light, fineness, warmth, being), the other negative. We might find this division into positive and negative poles simple except for one difficulty: which one is positive, weight or lightness? Parmenides responded that lightness is positive, weight negative. Kundera then questions “Was he correct or not?” The lightness/weight opposition remains the most ambiguous of all. Kundera then asks, should one live with weight and duty or with lightness and freedom? In Nietzschean terms, weight is life-affirming in that to live with positive intensity is to live in a way you’d be prepared to repeat. The emptiness of Sabina’s life in ‘The Unbearable Lightness Of Being’, and that she wanted to “die in lightness” — which is to say that she is indifferent to her life — shows that she would not want to repeat her life and would not accept an eternal return.