The theme of appearances as deceiving emerges in chapter 3 when Nick retreats to Gatsby's library. There, Nick meets the man in the owl-eyed spectacles, who points out that the library isn't exactly as it seems. Owl Eyes had expected the books to be fakes. They are real, but at the same time Gatsby's affectation is exposed when we realize he never reads these books, a fact that becomes clear when Owl Eyes notes the pages are uncut:

‘See!’ he cried triumphantly. ‘It’s a bona fide piece of printed matter. It fooled me. ... It’s a triumph. What thoroughness! What realism! Knew when to stop too—didn’t cut the pages.

The books in the library go far to characterize Gatsby. He is often almost but not quite telling the truth.

Nick applies the quote about affectations concealing something directly to Jordan Baker, believing he has gotten to the heart of what her cool exterior conceals. He remembers a scandal in which she was accused of cheating at golf. Though it is not clear whether she actually did or not--the caddy "retracted his statement" and the other witness decided he might have been mistaken, Nick nevertheless decides Jordan is a liar, stating: "She was incurably dishonest."

But even as Nick accuses Jordan of lying, he reveals that he himself lies to his girlfriend back home, for whom he a vague distaste, about their relationship. He moves from Jordan's dishonesty to thinking uneasily about his own situation:

I had to get myself definitely out of that tangle back home. I’d been writing letters once a week and signing them: "Love, Nick," and all I could think of was how, when that certain girl played tennis, a faint mustache of perspiration appeared on her upper lip.

Right after the statement above, a confession of dishonesty, he shows he is blind to his own affectation, which is that he is honest:

Every one suspects himself of at least one of the cardinal virtues, and this is mine: I am one of the few honest people that I have ever known.