How does "Soldiers Home" illustrate the "iceberg principle?"
Hemingway could have added a great deal of description of what Harold Krebs had gone through during the fighting in Europe in World War I, but he chose to focus on how Krebs was feeling after he returned to his home in Oklahoma. The reader can infer that Krebs had been through a lot of fear, stress, and actual horror from the way he is recuperating psychologically in his hometown. He spends a lot of time sleeping and reading. He sits on his front porch and watches the pretty girls passing by on the other side of the street--but he doesn't want to get involved with any of them because he craves peace, quiet, and solitude. Getting involved with a girl would get him involved with human emotions, and he has experienced too many strong emotions, especially for such a young man. Getting involved with a girl would get him involved in the town's social activities. He hardly seems to want involvement with his own parents or his sisters. He has seen the worst of humanity, and it will take some time for him to readjust his perspective.
The most important events in Krebs's recent life all took place in Europe. Hemingway understands what these events were like, but in accordance with his so-called "iceberg theory" he leaves those events out of his story. He could easily have described one or two of Krebs's nightmares. No doubt a motion-picture version of the story would do exactly that. It would show a battlefield with flashing artillery booming and soldiers charging through barbed-wire entanglements, and then it would cut to Krebs waking up in bed with a look of terror on his sweaty face. Hemingway chose not to do anything like that, but the reader feels the horror of war through Krebs's psychological reaction to it.
"Soldier's Home" strongly resembles Hemingway's longer story "Big Two-Hearted River," which is ostensibly about a young man on a solitary fishing trip. The reader comes to understand, without being explicitly told, that the protagonist has been through a terrible ordeal in the war and just wants to spend time alone, doing what he likes best, and letting his mind heal. "Big Two-Hearted River" is fascinating in what it doesn't say.