How does Elizabeth judge Darcy?
In Jane Austen's Pride and Prejudice, Elizabeth Bennet allows her first impressions of Darcy--that he was snobbish and proud--to prejudice her against him. Consequently, she draws false judgments about his character and motivations. This prejudice is best manifested by her assumptions about Darcy's actions related to two events: the Bingley's courtship of Jane and his falling out with Wickham.
Darcy convinces Bingley to abruptly break off his budding romance with Jane. When Elizabeth discovers this, she assumes Darcy's intentions to be wholly nefarious and stemming only from class snobbery. She refuses (at first) to recognize that Jane appeared somewhat disinterested toward Bingley and that Darcy feared she would break his friend's heart. Likewise, Elizabeth misjudged Darcy's conduct toward Wickham. She accepted Wickham's gossip about Darcy (that he had swindled Wickham out of an inheritance) wholesale, not recognizing until later how improper it was for him to discuss such a matter with a new acquaintance. Due to her prejudice against Darcy, she is unable to see the flaws in Wickham's character until Darcy later tells her the truth about Wickham (and offers witnesses to corroborate his story).