In the first few selections of In Our Time, Hemingway continually brings up themes relating to idealism. This is highlighted mostly in the the stories about Nick Adams by the serenity of the woods and Nick's persistence in believing that things will get better. Juxtaposed with this are a gruesome cesarean section, the following suicide, and Nick losing the love of his life. It is clear that Nick uses denial and idealism to protect himself from these thoughts. This is shown initially when a young Nick feels confident that he won't die after watching someone else do just that and later when an older Nick tries to rationalize to himself the implications of losing Marjorie. He even goes so far as to delude himself that he could be with her again.
In the stories related to war and not Nick Adams, Hemingway presents a seemingly opposite theme, realism. Events are told exactly as they happen, with little emotional reaction or concern. Killing, famine, and hopelessness are expressed as common, every-day occurrences.
Hemingway is using parallelism to show that the way Nick tried to block out the reality of his situation is very similar to the cold, ultra-realistic tone in the war-time passages. Though idealism tends to look away from the problem and realism directly at it (in a physical sense that is) , when both are taken to the extreme neither can properly understand it. In the case of ultra -realism, it becomes quickly apparent that by sucking out the emotional impact and human element of even the most horrific event can make it seem trivial and insignificant. On the other hand, ultra-idealism overcompensates by looking only at the good sides of things and ignoring the bad. Both are the results of the human brain's self-preservation in that they both prevent negative emotions by either covering them up with good ones (idealism) or stripping out all emotion (realism).