According to Kundera, "being" is full of "unbearable lightness" because each of us has only one life to live: "Einmal ist keinmal" ("once is nonce", i.e., "what happened once might as well have never happened at all"). Therefore, each life is ultimately insignificant; every decision ultimately does not matter. Since decisions do not matter, they are "light": they do not tie us down. But at the same time, the insignificance of our decisions - our lives, or being - is unbearable. Hence, "the unbearable lightness of being".