From early on in the novel, it can be seen that Darcy falls victim to Elizabeth Bennet's "dark eyes," and yet it is clear that when he makes his first proposal, he may be in love with her, but his character has not changed in any way. However, Elizabeth's response to this proposal and the way that she rebukes him and challenges him gives him the necessary stimulus to examine himself and to develop and change in his character. When he finally proposes once again, and Elizabeth accepts him, note what he says about how he was brought up with an incorrect understanding of pride, and how Elizabeth was the character to make him realise he had to change:
Such I was, from eight to eight and twenty; and such I might still have been but for you, dearest, loveliest Elizabeth! What do I not owe you! 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.
Darcy comes to love Eliabeth sincerely by the end of the novel therefore because she is one of the only women to stand up to him and to teach him a lesson that leads to true development in his character. This builds on his earlier favourable impressions of Elizabeth to form a solid, lasting regard and love towards her.