Anna KareninaAnna Karenina, the first novel of Count Leo Tolstoy is about the life of Anna (mainly) and her lover Vronsky (I know it is not possible to say what the novel is about but for this particular discussion we can assume that the novel is about Anna and Vronsky).
In the earlier parts of novel (earlier means those early chapters when the readers don’t know for sure if Anna and Vronsky has fallen in love with each other) we, the readers, automatically take Vronsky as an immoral man, Why? Tolstoy never mentions the immoral side (if there existed any) of Vrosnky, we don’t find any history of debauchery or infidelity, all we find is that he is being compared to a hard working man, Levin. And he fell in love with a mother of child, Anna.