Omelas is a city where all the citizens live fulfilled and happy lives. There is no disease, crime, or sorrow of any kind. On reaching adulthood, every citizen is taken into the dungeon of a citadel where they find a child chained to the wall. The child is malnourished, sick, and in great pain.
They know that if the child were comforted, the magic of Omelas would wither, and disease, crime, and want would become a part of people's lives in Omelas. Those are the terms, everyone's happiness depends wholly on this child's abominable misery and all people are aware of this.
You are on Earth right now. There exists a button in front of you which would make Earth just like Omelas. The child who suffers would be randomly selected.