"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, that personification of absolute fortuity, now again lay beside him, breathing deeply."
Tomas and Tereza's entire romance is based on a string of chance events and coincidences, which frightens Tomas. Tomas thinks of Tereza as a woman born of "six fortuities" in his life, including the sickness of a doctor that brought him to her town, mentioned here, and the coincidences of his room number, books, and Beethoven. Returning to Prague for this woman means Tomas willingly gives up his career and the happiness he used to imagine for himself. It bothers him to think how utterly random it is that he fell in love with this particular woman and therefore had to sacrifice so much in his life. Tereza, on the other hand, thinks such coincidence are planned by fate, and make up the beauty of life.