"It must be. It must be." is a recurring phrase in Milan Kundera's novel "The Unbearable Lightness of Being," highlighting the existential theme that life is shaped by significant choices. Characters grapple with the weight of their decisions, suggesting that every action carries a sense of responsibility and consequence, profoundly influencing their destinies in a world that often feels random and fleeting.

This concept resonates throughout the narrative, emphasizing the idea that while life may appear light and free, the intricacies of love and betrayal add layers of complexity. Kundera invites readers to reflect on the meaning of existence and the burden or freedom that comes with each decisive moment, ultimately exploring the paradox of lightness and heaviness in human experience.