The person who had the greatest negative influence on Pip from the time he was a boy is Miss Havisham. She warps his mind into believing that the only way he can be happy is with Estella and as a gentleman.
From the beginning, Miss Havisham only brings Pip into her life as a plaything and test case for Estella. Estella is being raised to be cruel to boys and men, and Miss Havisham needs a boy for her to practice on. Miss Havisham also enjoys manipulating Pip.
[When] we were singing Old Clem, and when the thought how we used to sing it at Miss Havisham's would seem to show me Estella's face in the fire, with her pretty hair fluttering in the wind and her eyes scorning me… (ch 14, p. 75)
Miss Havisham makes him doubt himself and be ashamed of who he is.
In chapter 18, Pip learns of his “great expectations” from Jaggers. He assumes that his benefactor is Miss Havisham. It is a reasonable assumption. After all, she is the only rich person he knows.
When he visits Miss Havisham, Sarah Pocket is there. Miss Havisham asks her to stay. Her reaction when he tells her he is grateful for his benefactor is telling.
“Ay, ay!” said she, looking at the discomfited and envious Sarah, with delight. “I have seen Mr. Jaggers. I have heard about it, Pip. So you go to-morrow?” (ch 19, p. 109)
She does not tell him she is the benefactor, but she lets him believe it. This is mostly for Sarah Pocket’s benefit. She loves playing with her and making her jealous.