In a nut shell, Harold Krebs leaves his home town because he can no longer relate to any of the people around him. That includes his family.
Harold Krebs is a war veteran. Like most war veterans, Krebs has been changed by what he saw while fighting in World War I; however, nobody else around him has gone through that change. He knows firsthand the atrocities that were committed by both sides of the conflict. Unfortunately, nobody in his Oklahoma hometown knows about those horrors. Everybody around Krebs wants to glorify the war and treat Krebs like he is some wonderful conquering hero. The people around Krebs most definitely do not want to hear the truth; therefore, in order to talk to anybody about his experiences, Krebs is forced to lie.
Krebs found that to be listened to at all he had to lie and after he had done this twice he, too, had a reaction against the war and against talking about it.
His repeated lies about the war eventually begin to wear on Krebs, and he develops a distaste for the war, talking about it, and the people around him.
A distaste for everything that had happened to him in the war set in because of the lies he had told. . . Krebs acquired the nausea in regard to experience that is the result of untruth or exaggeration . . .
His feelings of discomfort toward his surrounding environment continue to grow. The saddest part of the story is that Krebs's own family is not a safe haven for him. He is forced to lie to his own mother. At the story's climax, Krebs tells her the truth and says that he doesn't love her or anybody. She begins to cry, and in order to make her feel better, Krebs reverts to telling another lie. He is sickened by it.
Krebs felt sick and vaguely nauseated.
"I know, Mummy," he said. "I'll try and be a good boy for you."
That moment is the last straw for Krebs. He can't stand the lying anymore. He decides that he will leave town, get a job somewhere else, and live a more solitary existence.
He would go to Kansas City and get a job and she would feel all right about it.
Krebs cannot forget his experiences during WWI. People in his hometown have romanticized war, but Krebs knows how horrible war is. He just can't tell anyone how terrible it is when all that the people want to hear is their glorified version of war. He accommodates them by telling lies about what happened in the war because he's trying to fit in to a society that doesn't understand what he's been through. It is his relationship with his mother that puts Krebs over the edge, and he realizes he can't stay with her in the town where he grew up. Mrs. Krebs still treats her son as a little boy, accusing him of not loving her when he won't do as she asks. Krebs responds by telling his mother he no longer has the capacity to love because of what the war did to him. When she cries, Krebs realizes he can never make her understand what he went through, and he lies, telling her he was just upset about something else. He tells her what she wants to hear, and he promises to be a "good boy". This event gives him the courage to leave and go somewhere else where people don't expect him to be what he was before the war.