In general terms, Amir is unable to escape his feelings of guilt in Khaled Hosseini's The Kite Runner. He makes many cryptic comments in the first few chapters of the book regarding what his guilt might be about, but it is not until chapter seven that we learn the specific cause of his guilt.
The opening line of the novel is heavy with import, as Amir writes:
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. Looking back now, I realize I have been peeking into that deserted alley for the last twenty-six years.
This is an interesting way to begin his story and it tells us many things. First of all, we learn that something significant, life-changing, happened to Amir when he was twelve years old. We have the time frame of the story, as well. Amir (we don't learn his name for a few pages) is writing about a past event from the benefit of time and perspective. The incident happened in 1975 and it is now 1981. Finally, Amir is still suffering the effects of that incident.
Even more ominous is Amir's pronouncement, after getting a cryptic telephone call from someone named Rahim Khan, that whatever happened in Amir's past he considers to be "unatoned sin." Obviously the author is using this technique is to create suspense and build to a revelation in chapter seven.
**If you have not read as far as chapter seven and do not yet need or want to know what the specific event from which Amir cannot escape is, stop reading now.
Amir's friend and family servant's son, Hassan, is being assaulted in an alley, and Amir makes a deliberate choice, a choice that has haunted him for more than a quarter of a century.
I had one last chance to make a decision. One final opportunity to decide who I was going to be. I could step into that alley, stand up for Hassan – the way he'd stood up for me all those times in the past – and accept whatever would happen to me. Or I could run.
This is the moment when Amir makes his life-changing decision, and the rest of the novel is a working-out of that moment and Amir's guilt.