One link between some of Katherine Mansfield's short stories and The Quiet American is the danger of idealism. In the works of both authors, naïve characters who live too much inside their own mental constructs end up suffering.
Examples of this in Mansfield include the stories "Miss Brill," "The Garden Party," and "Bliss." In "Bliss," the young and wealthy Bertha naively believes she is living the perfect life until she realizes her husband is having an affair with another woman. In "The Garden Party," Laura feels ashamed and upset as she is forced to acknowledge the reality of the class divide she wants to will away in her fantasy construct of life. In "Miss Brill," Miss Brill tries to turn her life into a childlike, happy story until she overhears gossip about herself that forces her to confront to reality of being a poor, lonely, and aged spinster living sadly in Paris.
In The Quiet American, the naïve, Harvard-educated American Alden Pyle is like the characters mentioned above in Mansfield's short stories. He reads books about Vietnam and is influenced by academic theories about what is best for Vietnam, but he doesn't actually know the first thing about the Vietnamese situation. He believes the US can save the Vietnamese from communism because such a belief aligns with his desires, not with the reality of the corrupt behavior of the anti-communist forces or the need of the West to leave Vietnam alone. He dies in the end because he cannot face the harsh reality of the way things really are.