Think about the location of Amir's scar. Hassan was born with a birth defect in the same location. What does it represent about Amir that he has placed himself in danger and come away with a scar in the same place? During all the years that Amir and Hassan were growing up together, who was really scarred and who was really a whole and good person? Hassan's scar did not stop him from being a good person and a good friend. The fact that Amir had no birth defect did not make him a good person or a good friend. So what does Amir's new scar, inflicted while he is being a good person and a good friend, represent? Is this some sort of external symbol that tells us anything about a change in Amir, that tells us anything about a way that Amir and Hassan are now equal, or that tells us something about how Amir and Hassan have become true brothers at last?