When other people perceive Anna's closeness with Vronsky as improper, Karenin then begins to wonder innocently if their relationship is in fact improper. Karenin's ignorance about Anna and Vronsky's intimacy is an example of dramatic irony:
Alexei Alexandrovich found nothing peculiar or improper in the fact that his wife was sitting at a separate table with Vronsky and having an animated conversation about something; but he noticed that to the others in the drawing room it seemed something peculiar and improper, and therefore he, too, found it improper. He decided that he ought to say so to his wife.
When the reader finally learns Karenin’s perspective, they realize he is completely in the dark about Anna’s blooming feelings for and relationship with Vronsky. The fact that Karenin is the last to realize what the reader and entirety of Petersburg society already knew is not only ironic but also somewhat pathetic. In turn, the reader begins to realize why Anna was unsatisfied in her relationship with Karenin in the first place. Karenin's obliviousness therefore further justifies Anna's dislike of him. This dramatic irony also proves Karenin's weakness as a character, as he cannot even perceive the change in Anna’s relationship with Vronsky like the rest of society.