Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
"The first duty in life is to assume a pose. What the second is, no one has discovered."—Oscar Wilde
"He who fears corruption fears life."—Saul Alinsky
What's up with the epigraph?
Toby gives us a double-whammy here, both of which have implications in the story. The first refers to young Jack's willingness to create his own identity—to tell people that he's something he clearly is not. Wilde suggests that that's what people do in life: that everyone is pretending to some extent or another, so it's okay if Jack does it. That's interesting because grown-up Toby doesn't seem to be entirely forgiving of young Jack's "Ima Be Who I Say I Am" shenanigans, but it's certainly in keeping with the book's tone.
The second one refers to a loss of innocence, which Jack experiences fairly early. He's quite the young hooligan, and clearly he gets a taste of the nasty side of life with Dwight. But again, the epigraph seems to write him a Get Out of Jail Free Card, since Alinsky says "hey, it's life." Young Jack was fairly big on getting away with stuff, so he probably would dig the implication.