Amir's unkindness is a recurring theme throughout the book "The Kite Runner" by Khaled Hosseini. One example is his treatment of his friend and servant, Hassan. Despite their close friendship, Amir often takes advantage of Hassan's loyalty and betrays him. One of the most significant examples of this is when Amir witnesses Hassan being sexually assaulted and chooses to do nothing to stop it, later resulting in his guilt and shame.
Additionally, Amir also demonstrates unkindness towards his father, Baba, whom he often feels neglected by due to Baba's strong personality and high expectations. Amir's resentment towards his father leads him to lie and manipulate situations to gain his father's approval, rather than being honest about his own feelings and shortcomings.