Amir's road to personal liberation and redemption requires him to return to Afghanistan and "finish things." He cannot remain isolated and aloof in the United States. In the need "to be good again" is rooted in having to confront his past and make right that which is right. The physical confrontation with Assef is a part of this. As he physically suffers, he smiles, knowing that he has been able to find redemption and liberation from his pain. The hare lip he endures is reflective of the only way for Amir to find liberation from his own guilt and his own failure, into a realm of redemption where his goodness is evident.
Walt follows a similar path in his own quest. He cannot remain aloof and separated from reality when he sees Sue in trouble and when he must help and guide Thao from the challenges that both face. Walt tells Thao that he "finishes things." One of these elements has to be his own redemption, something that has alluded him for quite a while. In the opportunity to help Thao, Walt must go back and confront the demons of violence that have haunted him. Just as Amir must go back and confront demons through violence and hurt, Walt must do the same. Through his own journey of redemption and personal liberation, Walt strives "to be good again." While the end result of each journey is different (Amir lives and Walt does not), both characters experience similar realities in seeking personal liberation and redemption.