Compare the relationships between Baba and Ali, and Amir and Hassan in The Kite Runner.
Although they all grew up together on the same property, the relationships between the two adults and two children ended quite differently in The Kite Runner. Baba had employed Ali as his servant for many years, and though they maintained a master/servant relationship, Baba always treated Ali kindly, as though he was a member of the family. Like Amir and Hassan, the two men had grown up together; Ali lived in a small hut outside Baba's fine home, and Baba did not consider Ali's Hazara heritage a roadblock in their relationship as many other Afghans did. Amir and Hassan grew up as playmates as well, and Amir shared most of his non-school hours with Hassan. However, Amir eventually grew jealous of Baba's attentions toward Hassan, and he plotted to undermine Ali's son by planting his own birthday gifts under Hassan's mattress to dishonor him. This deceitful act caused Ali and Hassan to leave Baba's home, permanently ending the relationship between the four.
For Baba, who had many friends and whose popularity in Kabul was widespread, the loss of his old friend Ali was probably not as devastating as it was to Amir. Amir had no other close friends, and he soon came to miss Hassan, though he felt his sinful actions were important to gain more attention from his father. Later in the story, we find that Baba has not been completely honorable to Ali when Rahim Khan reveals to Amir that Baba had actually fathered Hassan. Thus, both Baba and Amir committed sins against their loyal friends/servants, and both lived with the unspoken guilt for years afterward.