Fallout Shelter is fun, but only for a while; you tend to hit a wall once everyone's happy and you've built a lot of stuff. This would be the point most people uninstall the game, or at least ignore it, but HarrisonHutcheon had something more drastic in mind.
"So I reached a plateau in my vault's development at 52 dwellers", they wrote in this imgur post. "Nobody wanted for anything and everyone was happy. I mindlessly collected resources every once and a while and the vault dwellers worked blissfully away at their jobs."
"This would not do."
So they hatched a plan: send every single dweller out into the wasteland. Only the ones who survived the night would be allowed back in.
Some were experienced adventurers with sweet gear and decent weapons! Others were soft workers from the deep, sent to their deaths with nothing but their fists and the shirts on their back.
I won't spoil everything for you, but hey, you can probably guess that the wasteland being the wasteland, things don't go well for most dwellers.