Amir is displeased that Hassan gets more attention, affection and love from Baba than he does. He develops intense jealousy that makes him loath the sight of Hassan even though Hassan loves Amir, and looks up to him in every aspect
Assef believes that all Hazara's are of the lower class and only the Pashtun's own and deserve to reside in Afghanistan. Out of hatred and to impose his superiority, he cold heartedly rapes Hassan who is physically unfit to hinder the problem.
Hassan is unfit to go through the learning process by attending school. He is illiterate; unable to read or write
Amir, knowing that his "friend/brother", Hassan was in need of his help, when being victimised by Assef, hesitated and even in the end did not decide to get involved to help Hassan because his strong sense of jealousy that overpowered the ability to want to provide help when something very wrong was happening and later feels guilty
Hassan was not able to defend himself as he did not know how to retaliate or fight back, like Amir, when provoked and gave in to the feeling of inferiority
Hassan, after the brutal incident of being raped by Assef, who considers his kind to be superior, is left with nothing but distrust as such a thing happened to him by the people of his own and doesn't know if anyone can be trusted hereafter