The main theme of the novel is that perception is not reality. Elizabeth's prejudice and Darcy's pride are both forms of blindness.
Elizabeth forms an implacable prejudice against Darcy the first time she encounters him. She overhears him saying she is not pretty enough to tempt him to dance. This, coupled with his other standoffish behavior at the assembly, causes her to decide he is an arrogant, insufferable jerk. Elizabeth's initial dislike then motivates her to be more than willing to believe the worst about him. Rather than weigh the evidence rationally, when the charming and attractive Wickham tells a sob story about being cheated out of a comfortable job promised to him by Mr. Darcy, she is quick to believe Darcy behaved badly. This is an example, well ahead of the term being coined, of confirmation bias: Elizabeth has decided, on scanty evidence, that Darcy is a jerk, so she readily jumps on whatever confirms her bias.
Darcy's pride likewise blinds her to the reality that Elizabeth and her family might be equal to him as human beings, even if they have less money and, in the case of some of her family members, less polished manners. He wounds and completely infuriates her in his marriage proposal, which assumes that a lowly person like her will naturally want to marry a great man like him. He more or less tells her he will deign to take her despite her lack of money and her embarrassing relatives. This throws her into such a fury that she tells him she, in effect, wouldn't marry him if he was the last person on earth.
It is not until Elizabeth learns to become less prejudiced against Darcy that she can see his true worth. Likewise, Darcy has to get off his high horse to be able to see that Elizabeth and her family are owed greater respect. When this happens, the two, now more mature, can happily wed.