The Unbearable Lightness of Being
How we cite our quotes:
"I know a precedent," said Tereza. "When I was fourteen I kept a secret diary. I was terrified that someone might read it so I kept it hidden in the attic. Mother sniffed it out. One day at dinner, while we were all hunched over our soup, she took it out of her pocket and said, 'Listen carefully now, everybody!' And after every sentence, she burst out laughing. They all laughed so hard they couldn't eat." (4.2.5)
Think about what a word like betrayal means to Tereza as opposed to Sabina. This passage is rather carefully placed after a long segment discussing Sabina's understanding of and attraction to betrayal.
When a private talk over a bottle of wine is broadcast on the radio, what can it mean but that the world is turning into a concentration camp?
[…] A concentration camp is the complete obliteration of privacy. (4.4.2-3)
This is presented through Tereza's eyes. Because she values privacy, we can see why Tomas's affairs bother her so much. In a way, by extending his sexual life to so many other women, he makes he and Tereza's private life public. He violates her privacy.
Oddly enough, the touch of his hand immediately erased what remained of her anxiety. For the engineer's hand referred to her body, and she realized that she (her soul) was not at all involved, only her body, her body alone. The body that had betrayed her and that she had sent out into the world among other bodies. (4.16.12)
Tereza feels that her body betrayed her by failing to become the only body in Tomas's life. Her actions now are an attempt at paying it back – at betraying her body – by rejecting it as something separate from her soul and subjecting it to objectification at the hands of the engineer.