Well, as an adult Amir is not very proud of himself as a child, what he did and what he didn't do. He's ashamed of how little respect he showed his father and how wrong he turned out to be about him.
His return to Afghanistan and taking in Sohrab, the child of the friend he'd forsaken, is his way of getting rid of the guilt and the shame and making up for his past flaws and thus receiving self fulfillment.
In my opinion his father is a far more interesting character, but it's been a while since I read the book, so I can't really say how he pursues self fulfillment. Perhaps by doing what he thinks is RIGHT and FAIR, going against what is wrong no matter what the cost to himself or his loved ones (the truck scene comes to mind, and how kind he was to the Hazaras, despite how they were thought of in society).
