The phrase is - The Unbearable Lightness of Being. It’s the title of a movie. It refers to a concept in philosophy that we have only one life and that the things that happen to us occur only here. Therefore, this life and the things in it are”light” or without significant meaning. The people in the movie who most live like that and treat people, relationships, and sex that way feel like they are more liberated or advanced. In the end, though, they find that way of life to be unsatisfying. Ultimately, life is unbearable without meaning.

I’m not sure what you mean. People don’t really say that phrase ever. It’s just the title of a movie.

What is the context?