It is human nature to expect great things of ourselves, especially when we are young and our life is just beginning to unroll. Pip is like any other young man who wants more than what he was born to.When he comes into a great deal of money, he has the ability to change his life and become a gentleman. That he thought Miss Haversham was the source of his fortune leads Pip to believe that means Estella to become his wife. This is pretty exciting for a young man who had no prospects beforehand.
Imagine that it were you to whom this fortune had been given and with it, the assumption that your benefactor was "giving" you a young lady's hand in marriage. You can imagine how shocked Pip is to discover that the convice, Magwitch, is his benefactor.
Pip receives this money and see it as a way of making his dreams come true: nice clothes and home, social status, a beautiful wife. Remember that Pip's first visit to the Satis House leaves him uncomfortable. This is when he actually understands that he's nothing more that a common laborer, but in the end, he also realizes that none of those things (the money, the clothes) have brought him the happiness and contentment that he experienced in the marsh. The money didn't make his friends love him any more than they already did; his pretentions made Estella laugh at him and shows him that this life of "great expectations" isn't what he wants.