Why do you think Jaggers believes Pip will not make anything of his good fortune?

When Pip meets with Jaggers, his new "guardian", Jaggers gives Pip all sorts of instructions about how he is to get his money, how he is to work with Wemmick, where he is to live, with whom he is to study, etc., and then he ends up telling Pip that he expects Pip to fail. He says:

"Of course, you'll go wrong somehow, but that's no fault of mine."

Jaggers proves to be a keen observer of human nature. He is an astute attorney who notices things that others do not. The nature of his work brings him into contact with the lower echelons of society -- criminals -- and he does not seem to have much faith in human beings. Plus, he knows where Pip came from. He has seen Pip as a boy at Miss Havisham's. He knows he is poor and lived with an uneducated blacksmith. He knows that when young people come into huge amounts of money without earning it, they are often frivilous with it and thereby lose it eventually. He also knows where the money came from, a convict, NOT Miss Havisham as Pip suspects.

As it turns out, Pip does fritter away his money. After not being in London for very long, he incurs huge debts, thereby proving that Jaggers was right.