This chapter – simultaneously – develops Amir's relationship with Hassan and Amir's burgeoning interest in writing. Coincidence? Probably not.
Amir tells of the story of Ali: Two wealthy young men high on hashish accidentally run over a Hazara husband and wife. The judge orders the men to enlist in the army; in an act of kindness, the judge adopts the orphan left behind by the Hazara couple. This judge is Amir's grandfather. Ali and Baba grow up together.
Amir launches into a discussion of ethnicity and friendship. On the one hand, he and Hassan are from different ethnic groups and have history and society in between them. On the other, they have the same nurse and grow up together in the same household. Amir doesn't come to a conclusion whether ethnicity drives a wedge between him and Hassan.
What follows are a few warm-and-fuzzy stories about Amir and Hassan growing up together.
The boys throw pebbles at goats
They go see Westerns at Cinema Park and they go to the bazaar.
Hassan prepares meals for Amir, makes Amir's bed, and polishes his shoes.
Amir reads stories to Hassan on a hill north of Baba's house.
Amir plays a few "harmless pranks" on Hassan. He tells Hassan "imbecile" means "smart, intelligent" (4.20).
Amir and Hassan share a favorite story: "Rostam and Sohrab" from the Shahnamah. It's a story about a father who kills his nemesis, who actually turns out to be his son.
Amir plays another trick on Hassan. Instead of reading from a book, Amir starts to make up his own story, although he flips through the pages as if he's reading from them. Hassan loves it. This prompts Amir to write his first short story.
Amir, proud of his story, tries to show it to Baba. Baba isn't interested at all; Rahim Khan comes to the rescue and reads Amir's story. Rahim Khan even writes Amir a nice note about the story.
Emboldened by Rahim Khan's praise, Amir reads his story to Hassan. Hassan is enthralled and even tells Amir he'll be "a great writer" (4.55). However, Hassan points out a plot hole. Amir knows Hassan is right, but he's also angry. He thinks some mean things.