Identify the objects that move from fantasy to reality.
In this masterful short story that captures the fantasy life of an otherwise boring, mediocre individual, there is a clear shift from the real world of Walter Mitty to his fantasy world, where he is "proud and disdainful" and "Walter Mitty the Undefeated, unscrutable to the last." The short story features five such fantasy episodes, where something triggers off the fantasy in Walter Mitty's brain, such as an object. Likewise, at times the fantasy ends when the fantasy life impinges on the real life, for example, at the end of the first fantasy, when Walter Mitty the Commander speeding up to take his plane through a storm shifts to Walter Mitty the henpecked husband, who is driving too fast along the streets.
Other objects that trigger such shifts are when Mitty drives past a hospital (which begins his Doctor fantasy), a newsboy shouting out about a trial (which initiates Mitty the defendant), glancing at an old war magazine (which begins a war fantasy) and then lastly lighting a cigarette and leaning back against a wall, which takes us to the end of the story and Walter Mitty facing the firing squad.
What is key to focus on is how in the world of this day-dreamer the boundary line between reality and fantasy is incredibly porous, and Mitty escapes his humdrum existence (and his terrible wife) by a series of fantasies, effortlessly shifting back and forth from one to the other.