As I recall, the most obviously paradoxical character is Amir, who treats his childhood friend Hassan so extraordinarly badly. You must read the opening chapters to understand the bond between these two boys. Amir knows better than anyone how kind and intelligent Hassan is; it is Hassan who has defended Amir in the past. But when Hassan is raped by bigger boys, Amir does nothing to save his friend. To make matters worse, Amir begins resenting his own father's attentions to his friend, and actively works to get Hassan and his father ousted from their home, where Hassan and his father work as servants. When Amir's father, (Baba) refuses to make them leave, Amir plants a watch to make it look like his former friend is a thief.
The greatest paradox in the story is Hassan. Hassan has an almost mystical ability to read and understand Amir (examples, his dream before the kite competition, his confession that he likes his home (p.55) and Amir's confession; "That was another thing about Hassan. He always knew when to say the right thing" (p. 35)). This extends outside of Hassan's relationship with Amir. He is able to run misleading kites, and later in life, when the Taliban took over (p.197) he says "God help the Hazaras now", just before the announcement that the Hazara are massacred.But for all of this 'mystic foresight', Hassan seems completely baffled by Amir's emotions after witnessing the rape. He says "I don't know what I've done Amir agha. I wish you'd tell me. I don't know why we don't play anymore." (p.82). Surely someone with such insight into Amir, and into everything, should have understood Amir's emotions that day at the pomegranate tree (p. 86). He'd have understood that when Amir yelled 'Hit me back" it was because he "wished (Hassan) would give (him) the punishment he craved." Instead, the Hassan loses his great skills at interpreting his friend, and instead, makes matters worse when he picked up a pomegranate "and crushed it into his own forehead".Hassan's double character makes him the most paradoxical character in the story. It's a flaw in the book, a plot hole that is not satisfactorily explained.