What would be a good topic connected to relationships in The Unbearable Lightness of Being and how they change the characters?

The major relationship
that is explored within this book is that between Tomas and Tereza, and it is clear that their
relationship together has a massive impact on both of them. This is particularly true of Tomas,
who, in one sense, gives up so much so that he can be with Tereza. When he thinks about their
relationship, he is shocked to realise how much about it depends on chance and luck alone, as
the following quote suggests:

He had gone back to Prague
because of her. So fateful a decision resting on so fortuitous a love, a love that would not
even have existed had it not been for the chief surgeon's sciatica seven years earlier. And that
woman, thatof absolute fortuity, now again lay beside him, breathing deeply.

He sees Tereza as a "personification of absolute
fortuity," or, in other words, a result of complete chance and luck. At every stage in
their relationship Tomas is aware of the role chance and blind luck has played. Tereza, on the
other hand, sees that their relationship is a result of fate alone and is not disturbed by the
element of chance. For Tomas, however, Tereza represents a "fateful decision" that is
actually built on something that, to him, seems very precarious. He returns to Prague for her
and thus gives up his career and his dreams of happiness for her. The random element in his
relationship with her deeply disturbs him when he considers how much he has had to give up for
her. Therefore examining this relationship and its impact on Tomas, but also the different
perspective Tereza has about it, would be an excellent topic to explore in more
depth.