Pip is sad. He hates his home, because it reminds him of how far away he is from the wealth and privilege of Satis House.
He feels like a black cloud has settled just above his head, following him wherever he goes and, like a big, heavy curtain, has barred him from continuing on the path toward becoming a gentleman.
Sometimes, he looks at the marshes near his house, and he thinks that they are like a metaphor for his own future. They are flat, low, dark, misty, and they lead only to the ocean.
Narrator Pip interjects, telling us that his one consolation in life is that he never expressed this sadness and dissatisfaction to Joe while he worked for him.
When Pip is working in the forge at night, he and Joe will often sing "Old Clem," and Pip is reminded of having sung the very same song with Estella and Miss Havisham. Often, he imagines Estella looking in at him from outside of the smithy, and he feels uber ashamed of his lifestyle.