In Khaled Hosseini's The Kite Runner, one proverb/saying or realization (life lesson) comes from Amir:
I actually aspired to cowardice, because the alternative, the real reason I was running, was that Assef was right: Nothing was free in this world. Maybe Hassan was the price I had to pay, the lamb I had to slay, to win Baba.
The first part of the saying is that nothing is free: everything has a cost to it. The second part, which refers to kinship, is Amir's comparison of Hassan as a sacrificial lamb: that he has to pay the price of offering up Hassan to be harmed (and removed from his life) so that he can have a closer relationship with his father, Baba—something he wants more than anything (and feels he cannot have with Hassan in the picture).
Amir and Hassan both love the book Shahnamah. It is the story of Rostam and Sohrab (enemies) who discover, once Sohrab (Rostam's "nemesis") is mortally wounded, that Sohrab is Rostam's son—and his father has killed him. Amir is not sure what moves Hassan in hearing of Sohrab and Rostam's fate, but he finds little to concern about himself, with regard to the suffering of the father—for Amir believes that fathers truly want to hurt their sons, a reflection of kinship once again.
Sometimes tears pooled in Hassan's eyes as I read him this passage, and I always wondered whom he wept for, the grief-stricken Rostam who tears his clothes and covers his head with ashes, or the dying Sohrab who only longed for his father's love? Personally, I couldn't see the tragedy in Rostam's fate. After all, didn't all fathers in their secret hearts harbor a desire to kill their sons?
The last quote that deals with a lesson on kinship takes place when Baba (Amir's father) notes his disappointment to Rahim Kahn that his son is not what Baba wants him to be—noting that something is "missing" in him. Rahim says, "Children aren’t colouring books. You don’t get to fill them with your favourite colours." This means that a parent cannot make a child what he/she wants the child to be. The parent has the most important "power" of giving the child life, but what the child becomes is only partially in the parent's control. The parent must accept that the child will not necessarily be as the parent wishes.