How does Joe react when Pip tells him the truth? What does this reveal about Joe?

Later, Pip tells Joe the truth, and also confesses that he is embarrassed about being a "commoner" because of his attraction to Estella.

Joe reassures him that he is not common, he is uncommon small and an uncommon scholar. Referring to Pip's lies, he adds, "If you can't get to be oncommon through going straight, you'll never get to do it through going crooked."

THis tells us that Joe understands Pip. He knows what Pip wants to be and he is able to keep Pip grounded despite his eagerness to become a "gentleman".