I can't remember the last time I read a true novel of ideas like
The Unbearable Lightness of Being. Nominally about two couples dealing with each other and the aftermath of the Prague Spring, the story is a meditation on actions and consequences, language, body and soul, and life itself.* The narration Kundera uses is deceptively folksy, as if he is a charming storyteller relating the latest gossip, but he is constantly challenging his characters' (and our) assumptions.
The title is taken from a concept elucidated early on by Kundera -- the idea that because we have one life, that we cannot revisit decisions or "try again," consequences don't matter. One can float through life without giving a thought to how others are affected because what's done is done, and therefore irrelevant. Tomas spends most of his life guided by this principle and so convinces himself that his dalliances with woman after woman could not possibly affect his wife. Sabina takes a slightly different tack. Not only does she acknowledge the consequences of her betrayals, she revels in them and seeks them out without letting them affect her; in her own way floats through life equally "light in being." Nevertheless, what these two spend so much time avoiding does ultimately weigh them down, in ways they don't necessarily acknowledge.
Tereza, on the other hand, is quite weighed down -- by her mother's grotesque earthiness, Tomas's infidelities, her unconditional love for her dog, and ultimately her own inability to reconcile the tension she perceives between her body and her soul. This latter struggle of hers is the flip side of Tomas's infidelities, and both derive from the idea that the soul and the body are separate entities.
The story takes place during and after the Soviet conquest of Czechoslovakia, and Kundera has quite a bit to say about that, too, particularly the irrelevance of ideas, integrity, or even truth in the face of a determination to win at any cost (something that hit close to home in our current post-fact, "fake news" political landscape). This novel served as a stark reminder of how much ugly, petty, unrelenting evil Communism causes. Turns out, extreme ideologies also thrive without being weighed down by the actual consequences they generate.
*Just a few chapters into the novel, I wondered how one could possibly turn these ideas into a movie. Turns out, you can't, and Kundera was disappointed with the adaptation.