Darcy himself references how Elizabeth has been responsible for teaching him a very important lesson when they finally get together and he proposes and is accepted. After the long journey they have taken to get to this stage, they both reflect on the somewhat tortuous path that journey has taken them on, and Darcy says the following to Elizabeth, refering to his first proposal to her:
You taught me a lesson, hard indeed at first, but most advantageous. By you, I was properly humbled. I came to you without a doubt of my reception. You shewed me how insufficient were all my pretensions to please a woman worthy of being pleased.
Elizabeth therefore taught Darcy an important lesson about his pride and the need to be "properly humbled." In the same way, it is clear that Elizabeth has learnt an important lesson about prejudice and her tendency to be taken in by "first impressions," which was actually the former title Austen wanted to give to this book. She has also learnt a very hard lesson concerning how dangerous it can be to form an opinion of one's character based on a fleeting acquaintance, both in her relationship with Mr. Darcy and also in her relationship with Mr. Wickham, the former appearing to be worse than he actually is and the latter appearing to be favourable whilst concealing a bad character. What Darcy and Elizabeth teach each other then relates to the two vices they suffer from as expressed in the title. Darcy has his pride humbled by Elizabeth, and Elizabeth is forced to acknowledge how she has been unduly and unfairly prejudiced against him. The stage is set for two wiser individuals to come together and for a typical Austenesque happy ending.