Once again, where's the post-apocalyptic setting?
Oh, it's vague - deliberately I think. The people in the story were safe from "the burning lands," but it was implied that those lands were still actively engulfed in fire and no one could live there. I personally made the wild extrapolation, based on the burner practice of using the sun to burn their bodies, that certain areas of the globe were exposed to powerful solar radiation because of a damaged atmosphere.
So not exactly end of the world, but a huge refugee crisis. There's also a strong implication that population is way down because teenage students go to school not to learn, but to do factory work. So, a lot of questions left unanswered, but I think the sparse world building managed to suggest an atmosphere of global upheaval.
The difference between widely shared experiences and universal experiences is at the core of much of the discussion on this forum.
That's a really good point, and I think it's also at the core of this story. Everyone, including Nessa, shares the trauma of living in a world where the burning lands have devastated the population and high schoolers are compelled into factory work. But some people have, obviously, suffered a lot more and lost much more. Some of the refugees are literally unable to let go of the experience of being burned and transform their bodies into memorials of the burned lands, reliving the experience of their pain the whole time. And, humans being what they are, those with something still to cling to agree that the people who've lost less deserve more, and refugees are called scum and marginalized even more. So the extent to which the experience is shared is erased by those who aren't forced to face it and want to believe that it doesn't affect them.
I want to point out that Nessa has a private trauma too - it's implied, again pretty vaguely, that she has some kind of chronic illness and has been in pain for a lot of her life. "Nessa had banged her own head against walls to get the pain out of her head and chest, but it never worked — or rather it never worked for long enough, leading to a worse, moreish pain." So despite her landedness, it's not as if she's living such a privileged life because she's defined by a private illness.
She's sort of forced to hide her personal pain because of the much more visible pain surrounding her, so her self-harm is a way to show her pain outwardly. Charlotte contrasts this by sharing in the world-defining trauma of being a refugee from the burned lands, but preferring to keep her pain inside and try to forget. There's a huge gulf between their experiences, but something in common, too.
Also, my comment about the zombie apocalypse outburst was meant to be tongue-in-cheek. I'm entirely aware that most people do not think that way. Sorry if that seemed to be dictating experiences.