There are many kinds of conflict in Khaled Hosseini's The Kite Runner, some of which impact nearly every character's life. When the war begins and the Taliban come to Kabul, for example, every character is affected. When Ali's mother so cruelly denounces her son, Hassan, and leaves Ali, that family is forever changed. When Amir's mother dies, Amir is left with Baba, who is not an effective parent in many ways; this causes Amir great confusion about how to give and receive love. Conflict happens when Amir and his father come to America, as their lifestyle is dramatically different. Of course there is conflict between Assef and Hassan as well as between Amir and Hassan. And the list goes on.
While these are all real conflicts, Amir is the narrator of this story, and the true source of conflict in this novel centers around him. On a physical level, the conflict is caused by the fact that Baba has another son, Hassan, whom he loves. It is Amir's reaction to that knowledge, both intuitively before he knows the truth and after he knows it as a certainty, which is the greatest source of conflict in this novel.
Though Amir and Hassan are inseparable for the first years of their life, Amir is often jealous of him. Hassan is a genuinely good boy who is implicitly trusting of and unquestionably loyal to Amir; however, Amir often treats him poorly out of his jealousy and an innate unhappiness which often makes him mean and even cruel. Because he is so intent on earning his father's love (which is rather a lost cause until much later), Amir allows an unspeakable thing to happen to Hassan. This is the manifestation of Amir's jealousy of Hassan and his desperation for Baba's love--and it is the thing which haunts him for the rest of his life.
I became what I am today at the age of twelve, on a frigid overcast day in the winter of 1975. I remember the precise moment, crouching behind a crumbling mud wall, peeking into the alley near the frozen creek. That was a long time ago, but it’s wrong what they say about the past, I’ve learned, about how you can bury it. Because the past claws its way out. Looking back now, I realize I have been peeking into that deserted alley for the last twenty-six years.
While Hassan might still have been assaulted by Assef, Amir could have intervened and Hassan would not have had to live with the life-changing shame of such a foul deed. His life was forever changed by Amir's lack of action, though his loyalty to Amir is unwavering. Amir's life was also unalterably changed by his jealousy (which caused him to take a perverse pleasure in Hassan's humiliation) and inaction.
At the beginning of the novel, Amir says, “It may be unfair, but what happens in a few days, sometimes even a single day, can change the course of a whole lifetime...” But what happened in that single day was the culmination of Amir's lifelong jealousy of Hassan and Amir's desperate longing for his father's unconditional love.