Stiva sets the novel in motion, not only in terms of plot—as the domestic upheaval caused by his affair with the family's governess brings Anna to Moscow, and thus to Vronsky—but also in terms of theme. Stiva embodies the notion that life is meant to be lived and enjoyed, not repressed by duties. He lives for the moment, thinking about responsibility only later, as his constant financial problems remind us. His dazed reaction to being chastised for adultery is not so much regret at his wrongdoing but rather regret at being caught. Indeed, even after Dolly forgives Stiva, he does not stop carrying on with other women. He does not feel any duty toward his wife and family that constrains his freedom.
Despite Stiva's actions, the novel does not portray him as exceptionally villainous. On the contrary, he represents an ordinary man in 19th century Russia. He is kind and jovial and genuinely loves his wife and family, yet he feels entitled to have sex with whomever he pleases. This apparent paradox in his character highlights the patriarchal nature of Russian society at the time. Stiva is essentially free to enjoy himself, while his wife is expected to endure his affairs in good-natured silence. Stiva nonetheless hides his affairs because he recognizes that he has a duty to be faithful to his wife, however lightly he—and society—may regard that duty.
Stiva's affair with his family's governess sets the stage for Anna’s much more dramatic struggle between private passion and social obligation. Like Anna, Stiva seeks out love and satisfaction in any way that is personally meaningful for him. But the similarity ends there. Stiva is far shallower than his sister, and lacks her emotional self-reflection and passionate intensity. His love affairs are trifles to him, whereas Anna’s becomes a matter of life and death to her. Stiva is not a dynamic character in the novel—he does not change. He is never punished for his sins and never improves his behavior. In short, Stiva’s constancy brings into relief the extraordinary changes—moral, spiritual, and psychological—that Anna undergoes.