Even though Nick has been invited to the party, he has never met Gatsby and has seen him only from a distance. At the party, Nick falls into a conversation with a man at the party. After discussing the war a bit, the stranger invites Nick to go boating with him. Shortly after, the stranger identifies himself as Gatsby, which surprises and somewhat embarrasses Nick because he did not know. Gatsby immediately puts Nick at ease by apologizing for being a bad host, and then he smiles at Nick.
Nick's description of Gatsby's smile and his reaction to it conveys much about Gatsby's character and personality:
It was one of those rare smiles with a quality of eternal reassurance in it, that you may come across four or five times in life. It . . . concentrated on you with an irresistible prejudice in your favor.
After he assesses Gatsby's appealing smile, Nick then sees Gatsby in a different light:
. . . I was looking at an elegant young rough-neck, a year or two over thirty, whose elaborate formality of speech just missed being absurd.
Nick's separate observations capture two very different aspects of Gatsby's character, very different but equally true.