When Assef, a Pashtun boy, asked Amir "[h]ow can you call him [Hassan] a 'friend'?"(41), he tried to deny the friendship with Hassan. This shows Amir had resistance to being considered equal to Hassan who had lower social status. Also, Amir was jealous of Hassan because his father, Baba, praised Hassan's courage to stand up for Amir while he could not do it even for himself. On the other hand, Amir did not envy Assef in the same way he envied Hassan, though Baba praised Aseff, too. This is because Amir just could not bear feeling inferior to a lower class person. Moreover, "[Amir's] favorite part of reading to Hassan was when we came across a big word that he [Hassan] didn't know"(28), and he felt a sense of superiority by teasing him. When Hassan was raped and suspended for stealing a watch, Amir justified his action of betraying by the fact that they lived in different classes. As these parts show, difference of class disturbed development of the relationship between Amir and Hassan even though they had faith in each other, and they could not create a fair relationship because of it.
Baba forced Hassan to be the son of a Hazara servant because he valued his dignity and honor more than the family tie with his own child. After Baba and Hassan died, Amir finally knew the truth that Hassan was not son of Ali, a Hazara servant, but son of Baba. Rahim Khan, Baba's old friend, said to Amir that it was because Hassan's mother was a Hazara and the situation was very shameful for Baba. In other words, Baba was afraid that he would lose his honor because of the fact that he had a Hazara son. So he chose to raise Hassan in poverty and put him into a hard environment in which he was likely to be discriminated, instead of raising him as his own son and giving Hassan his wealth as he did to Amir. Eventually, Baba's decision caused Hassan to leave his house and to remain in Afghanistan while Baba and Amir escaped to America during the war.