MacCready winds up at Little Lamplight, probably a baby, but at most young enough not to remember his parents. Maybe he grows up with a secret belief that they loved him, because they left him with three names whereas a lot of his peers didn’t get any. But they were grown-ups, so who needs them anyway.

He grows up eating fungus that thrives on human flesh. He starts drinking at six. He learns to shoot at ten — starting with monsters who used to be human, but undoubtedly graduating to humans long before he should have. Also at ten, he wins a fight against another child and takes power as mayor. Part of the job is to exile kids when they turn sixteen. Maybe some of them helped raise him. He knows Bigtown isn’t as safe as it’s made it out to be, how could he not? A lot of those teenagers are headed out there just to die. MacCready knows he won’t be one of them, because he’s tougher.

When we meet him at twelve, he’s ruthless. He admits that the out-at-sixteen rule is based on lies, and that it’s really to keep the population low enough to survive. He’s a social Darwinist who protects the kids as a population, but can’t afford the luxury of caring about them as individuals. He’s learned death is cheap, you can’t afford to help strangers, and if you don’t take what you want, someone else will.

“Around” sixteen he graduated (which makes me think he left before they could kick him out), and we know the rest of the story. The person we meet in Boston has internalized these lessons. He’s friendly and has a conscience, but the only people he cares about enough to prioritize are Duncan, a maxed-affinity Sole Survivor, and probably a few others like Daisy. And boy, does he care about that tiny group of individuals. But everyone else? Make it worth his while or go kick rocks.

Having a crazy childhood doesn’t fully explain his choices - encouraging the Survivor to kill Danse, cruelly flirting with Desdemona as the Survivor betrays and murders her, outright stating he’s willing to kill innocents if there’s a way to profit from it, and disliking giving the cure to Austin even though his son is in the exact same situation. But I think his history goes a long way toward explaining his motivations and making him likable, if not exactly justifiable.