Without a doubt the most important event in these chapters occurs in Chapter Seventeen, which is when Amir goes and visits Rahim Khan in Pakistan and discovers the truth about his relationship with Hassan. Rahim Khan tells him that Hassan was actually Amir's half-brother, the result of an illicit coupling between his father and Hassan's mother, who was married at the time. The impact of this revealed secret is momentous on Amir. Note how he responds:
I'm thirty-eight years old and I've just found out my whole life is one big fucking lie! What can you possibly say to make things better! Nothing. Not a goddamn thing!
Of course, this relationship with Hassan makes Amir's childhood betrayal even worse, which in turn makes Amir feel obliged to do what he can to rescue Hassan's son from Afghanistan and save him. Thus this revelation is of major importance for the structure of the plot, as it is the catalyst that sends Amir back to his homeland, and, though he does not know it at this stage, to redeem himself by facing Hassan's persecutor to save Hassan's son.