People pay for what they do, and still more, for what they have allowed themselves to become. And they pay for it simply: by the lives they lead. —James Baldwin
Technicalities first: this epigraph comes from James Baldwin's book No Name in the Street, which is a book-length autobiographical essay on race, Western society, and the Civil Rights Movement.
Bastard Out of Carolina is, in some ways, about the bad characters not getting their comeuppance: Glen gets beaten up by the uncles once, sure, but that doesn't stop him from raping Bone and getting Anney back afterwards. In the end, Anney, too, while she clearly suffers, still gives up her daughter to be with her lover, and she's not even a bad guy.
Poor Bone, the victim of all of this, is the one left motherless. Naturally, we the readers want to cry out, "Where's the justice in that?"
That's where the epigraph comes in. No, a satellite isn't going to fall from the sky onto Glen as a symbol of divine justice to make us feel better. Baldwin's quote says that nobody really gets away with things, even if it might seem like they do. A person who does bad things will not lead a happy life, plain and simple.
We don't even have to take it that far, actually. Take Anney, for example. She doesn't really do "bad" things, at least not intentionally, and not to the extent that Glen does. Even so, she has to live with the decisions she's made, and we can tell that's not going to be easy for her; she'll probably never forgive herself. That's a pretty bad punishment in and of itself.
Glen, a guy we really want to see punished, can't keep a job, can't take care of his family, is a failure in the eyes of his father, and has permanently polluted his relationship with Anney by beating and raping Bone. He'll probably never get past this; he'll always be stuck in a world severely limited by his bad acts and bad choices.
This novel shows us how important it is not to become someone who will be incapable of leading a good life. Even Bone risks becoming a hateful and judgmental person (see the "Foil" section under "Character Roles" for more). Doing bad things, or letting negativity overtake you, makes it difficult to find happiness and live well.
If Glen and Anney were to ride off into the sunset smiling and laughing, then we might think: "Gee, I guess sometimes bad acts go completely unpunished." If their car were to go off of a cliff at the end of the novel, we might think: "Gee, the idea that bad acts always have a punishment is really over-the-top and unrealistic." Instead, the epigraph helps us understand that that there is punishment, but it is punishment that needs to be quietly understood rather than shown.