Many characters in the novel perceive things in a way that is not accurate.
The most obvious example of perception versus reality is that of Gatsby's view of Daisy.
He holds an idea of Daisy in his mind, but the reader can see that she is not a worthy object of worship.
Nick believes that even Gatsby can't maintain the dream. When Daisy doesn't get in contact with him after the accident, he imagines that Gatsby:
"shivered as he found what a grotesque thing a rose is".
The symbolism of the flower clearly suggests he feels disillusioned with Daisy.
The eyes of Doctor T. J. Eckleburg
These giant eyes also symbolise the idea of false perception. They are the remains of an ancient advertisement for a company that no longer exists, they loom emptily over the wasteland that is the valley of ashes. In his grief, George Wilson confuses them with the eyes of God.
To begin with Daisy either overlooks, or doesn't notice or care that Gatsby fails to conform to how a gentleman should behave.
Ultimately she does choose Tom over Gatsby because of Gatsby's connections to the criminal underworld and his lack of connections with the upper class.
Tom, on the other hand, is very much of the upper classes, and has always been this way:
Even at college his freedom with money was a matter for reproach… he'd left Chicago and come East in a fashion which rather took your breath away; for instance, he'd brought down a string of polo ponies from Lake Forest.
Gatsby attempts to pass himself off as belonging to the old money set, for example, by calling people 'old sport'. But these attempts are a failure. Nick observes that his "elaborate formality of speech just missed being absurd"; Tom laughs at the suggestion that he studied at Oxford, picking up on the fact that Gatsby does not wear the 'right' clothes':
An Oxford man… Like hell he is! He wears a pink suit.
He also fails to pick up on subtle social signals, such as when he is invited home for lunch by the Sloanes and they don't really want him to come.
During this same scene Gatsby is alienated from the Sloanes and the Buchanans by the fact that he doesn't own a horse. This emphasises the old money/nouveau riche divide:
The vulgarity of his West Egg house contrasts with the tasteful Colonial opulence of the Buchanans' mansion in the more exclusive East Egg: "an imitation of some Hôtel de Ville in Normandy, with a tower on one side, spanking new under a thin beard of raw ivy"
Other class divisions are emphasised, too: Myrtle Wilson would like to move in Tom's social circles but this would never be possible. It has been said that in the novel there are three classes: