“The Ones Who Walk Away from Omelas” (Variations on a theme by William James) is a 1973 short story by Ursula K. Le Guin. It is a philosophical parable with a sparse plot featuring bare and abstract descriptions of characters; the city of Omelas is the primary focus of the narrative. 
In the story, Omelas is a utopian city of happiness and delight, whose inhabitants are smart and cultured. Everything about Omelas is pleasing, except for the city’s one atrocity: the good fortune of Omelas requires that a single unfortunate child be kept in perpetual filth, darkness and misery, and that all her citizens should be told of this upon coming of age.
After being exposed to the truth, most of the people of Omelas are initially shocked and disgusted, but are ultimately able to come to terms with the fact and resolve to live their lives in such a manner as to make the suffering of the unfortunate child worth it. However, a few of the citizens, young and old, silently walk away from the city, and no one knows where they go.
The story ends with…
“The place they go towards is a place even less imaginable to us than the city of happiness. I cannot describe it at all. It is possible it does not exist. But they seem to know where they are going, the ones who walk away from Omelas.”