The novel centres around four main characters ~ Tomas, a philandering surgeon; his wife, Tereza, a country waitress turned photographer; Sabina, an artist and mistress of Tomas; and Franz, a Swiss lecturer and Sabina's lover. The story that unfolds is set in Czechosloavkia between the Prague Spring in 1968 and the mid-70s. It is a story that deals with the weighty topics of love, sexual desire, political action, the meaning of life and happiness. Kundera uses the German adage 'einmal ist keinmal' (what happens but once may just as well never have happened) to suggest that life is essentially 'light' and ephemeral and it is this lack of weight or purpose that gives the novel its name.
It was interesting to read this book again after a long time, since I was a university student back then and now have much more life experience and maybe now react to it in a different way. Certainly one of my favourite books and maybe I will wait less time before reading it again.