The book repeatedly discusses the themes of lightness and weight.
As used in the book, if one is experiencing lightness, they are approaching life with nonchalance, flippancy, or easygoingness. Nothing is all that important, and nothing has to happen a particular way. A million paths open up to you each morning, and you can take whatever one you feel like. Lightness abounds when commitments are few. Tomas’ philosophy is that “the only relationship that can make both partners happy is one in which sentimentality has no place and neither partner makes any claim on the life and freedom of the other”. Erich Fromm espouses a similar idea in Escape from Freedom, though I can’t remember what he calls it (something like “voluntary cooperation of free agents”).
Weight in this context means gravity, fate, purpose, or duty. Things must happen. Things must be done. Love is possible when actions and events have weight. Commitment becomes viable, because the parties in a relationship have something heavy preventing them from leaving on a whim. Weight doesn’t guarantee fun, but it may make deeper fulfillment possible.
I am hopelessly biased, but Kundera is as well.
There is a time for lightness–a time for merrymaking, enjoying the smell of the ocean, and being spontaneous. However, from my experience, I must reject this flippancy as being the main theme of human life. While Kundera acknowledges that his characters have a need for love, meaning, constancy, and worship in their lives, I get the sense that this is only ‘one weird trick’ for living out one’s days with minimal despair. In his broader view, nothing appears to mean anything. The title of his book could be rewritten as Life Has No Meaning and You Will Never Quite Come to Terms with that Fact.
The parts I found most valuable, aside from his striking character sketches throughout, were in the chapter “Lightness and Weight”, sections 2-7 & 13-15. These detail Tomas’ interactions with authorities in Soviet Czechoslovakia, and discuss how honest upbringing is a liability during secret police interrogations. The later sections deal with the movement resisting Soviet occupation, which Tomas’ son is a part of. There’s a lot of agonizing over whether signing a paper does anything. Tomas at one point loses his job as a surgeon for refusing to sign a statement condoning Soviet power. Later, he refuses to sign a public statement being put out by the resistance. Another character Franz, in similar predicaments, eventually decides that when there is no possibility of action against evil, playacting is better than inaction: “His true goal was not to free the prisoners; it was to show that people without fear still exist.”
Kundera also makes a lot of funny assertions about creation, original sin, the Imago Dei (whether God has intestines), and whether animals have souls. For most of his rambling inquiries he presents what he believes to be the two possible answers, but they seem like false dichotomies.
All in all, The Unbearable Lightness of Being is a very peculiar book.