Nick, like many first person narrators, is unreliable. He is more dishonest than he believes. As the novel opens, he goes to dinner at his cousin Daisy's home, where Daisy and Tom insist they have heard rumors that he is engaged. He denies this vigorously, but it is clear later in the novel that he is more entangled with a woman from Chicago than he wants to admit. While insisting that his "cardinal" virtue is honesty (!), he thinks uneasily about Jordan and the fact that he is still writing happily to the midwest girlfriend as he grows more and more attracted to Jordan. He vaguely dislikes this midwest girlfriend, too, noting the distasteful line of sweat that appears above her upper lip after a game of tennis, but doesn't appear honest enough to make a clean break with her.
Nick claiming honesty as his virtue is also a sign of dishonesty: honest people, paradoxically, tend to be honest enough to question their own veracity and to show awareness that they might have blind spots.
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