"In Great Expectations, Pip is embarrassed by Joe, because he's crude and Pip is on the way up. Reading it, you ask yourself, what is it like to be Pip and what's it like to be Joe? Would I behave better than Pip in his situation? It's the spaces which emerge between the two characters where empathy occurs."
I guess this could explain the earlier quote, about how the incompleteness of one character help us understand the others. This incompleteness would be this space in between that makes us consider what is it like to be either of the characters.