What is the significance of Amir visiting the orphanage built by his father later in the book?
Much of the development of Amir's sense of himself comes from the trip to Afghanistan and finding out the true story of his brother Hassan and his father's life. In this case, the fact that his father's orphanage was destroyed could be interpreted as symbolic for the fact that his father's attempt to care for Hassan who would have been an orphan in other circumstances also fell short despite his greatest efforts. The discovery of the fact that his father's orphanage was destroyed is juxtaposed against the visit to the working orphanage to search for Sohrab.
Here Amir is furious with Farid, the director, when he learns that he has been willing to basically sell children to the Taliban in order to get some money for food and other necessities for the other children. Here too the futility of a good man's best efforts are demonstrated with the horrid circumstances and terrible choices Farid has to make when it comes to taking care of the children.