Answers 1Add Yours
If you are referring to chapter 14, Pip explains his misery to his readers: He is ashamed of his home, ashamed of his trade. He wants to be uncommon, he wants to be a gentleman. He wants to be a part of the environment that he had a small taste of at the Satis House.
His greatest fear allies his greatest shame. He fears, beyond everything else, that Estella will see him in his current, dirty, blacksmith state. If he achieves "bettering himself" he will lose what makes him Pip in the first place.