The character of Fitzwilliam Darcy is meant to be passive and contemplative. This is the exact opposite of his counterpart, Elizabeth, who is the active and dynamic version of Darcy. This being said, it is known that Darcy's intellectual and analytical nature combined with his own pride and prejudice keeps him from socially interacting and, instead, he gets to self examine his reactions and those of others.
Meanwhile, Elizabeth's intervention in his life is to expose his own weaknesses, and to openly illustrate to him his flaws. Because he was open to listen, and was able to clearly see what his problem with pride and his prejudices are. This is how he began to change and eventually see things from Elizabeth's perspective.