I think that the individual's response to injustice is one of the critical elements of the novel. Amir's fundamental guiilt, the need to "become good again," lies in how he watched Hassan brutalized and failed to do anything about it. He did not respond to injustice, and while he has moved on with his life, there is a lingering pain and doubt that he let a moment slip by in his consciousness. His return to Afghanistan and eventually being led to Sohrab is a moment where Amir is confronted with injustice. Consider that Sohrab is being held captive by Assef. Once again, Amir is confronted with an instant of injustice, this time with the son being imprisoned. The fact that Amir encountered injustice in two generations, father and son, is what drives him to do now what he should have done then. The confrontation between Amir and Assef is a reflection of how the novel demands that individuals rise and take action against injustice. It suggests that individuals cannot sit by passively for long when it is evident that someone else is engaged in struggle or when it is truly apparent that there is pain and suffering that requires intervention for alleviation. It is this motivation that compels Amir to fight Assef to save Sohrab.