Challenging the concept of eternal recurrence (the idea that the universe and its events have already occurred and will recur ad infinitum), the story's thematic meditations posit the alternative: that each person has only one life to live and that which occurs in life occurs only once and never again – thus the "lightness" of being. Moreover, this lightness also signifies freedom; Tomáš and Sabina display this lightness, whereas Tereza's character is "weighed down". In Constance Garnett's translation of Tolstoy's War and Peace she gives us the phrase "strange lightness of being" during the description of Prince Andrey's death. In contrast, the concept of eternal recurrence imposes a "heaviness" on life and the decisions that are made. Nietzsche believed this heaviness could be either a tremendous burden or great benefit depending on the individual's perspective.[3]
The "unbearable lightness" in the title also refers to the lightness of love and sex, which are themes of the novel. Kundera portrays love as fleeting, haphazard and possibly based upon endless strings of coincidences, despite holding much significance for humans.
Quoting Kundera from the book:
The heavier the burden, the closer our lives come to the earth, the more real and truthful they become. Conversely, the absolute absence of burden causes man to be lighter than air, to soar into heights, take leave of the earth and his earthly being, and become only half real, his movements as free as they are insignificant. What then shall we choose? Weight or lightness? ... When we want to give expression to a dramatic situation in our lives, we tend to use metaphors of heaviness. We say that something has become a great burden to us. We either bear the burden or fail and go down with it, we struggle with it, win or lose. And Sabina – what had come over her? Nothing. She had left a man because she felt like leaving him. Had he persecuted her? Had he tried to take revenge on her? No. Her drama was a drama not of heaviness but of lightness. What fell to her lot was not the burden, but the unbearable lightness of being.[4]
In the novel, Nietzsche's concept is attached to an interpretation of the German adage einmal ist keinmal 'one occurrence is not significant'; namely, an "all-or-nothing" cognitive distortion that Tomáš must overcome in his hero's journey. He initially believes "If we only have one life to live, we might as well not have lived at all," and specifically (with respect to committing to Tereza) "There is no means of testing which decision is better, because there is no basis for comparison." The novel resolves this question decisively that such a commitment is in fact possible and desirable.[5]
