Why does Mr. Collins decide he wants to marry one of the Bennet daughters in Pride and Prejudice?

William Collins is a clergyman and cousin to Mr. Bennet. He has a sense of what is proper and acceptable and also seems to exude an exaggerated sense of self-importance. Because his social skills are lacking, he seems to think that the first young lady he meets that he finds agreeable should agree to be his wife. He sets his sights on Elizabeth because she is genteel, attractive and intelligent, and because of his connection to the family he feels entitled to expect her acceptance. Because Elizabeth is polite to him, he mistakes this for reciprocity of his affections, and even insists that she refuses his proposal out of a sense of propriety, because she secretly does wish to marry him. Oddly enough, this is similar to the behavior Elizabeth displays towards Mr. Darcy when she first rejects his proposal. Mr. Collins' lack of sensitivity and social boorishness make him a completely inappropriate match for Elizabeth, but on some level he is a more caricatured version of Darcy, who is also somewhat awkward socially and not as comfortable with the social niceties that are expected of gentlemen in Austen's milieu.