Where is the symbolism in "The Secret Life of Walter Mitty"?

I would want to answer this question by pointing out the
way in which Mitty, in his desperate desire to escape from his humdrum existence and his
terrible wife, gives normal, everyday objects and actions symbolic significance as they
trigger off his series of daydreams. Note the way in which driving past the hospital
after he has dropped off his wife symbolically gives rise to his daydream about
performing a major operation. Likewise hearing a newsboy talking about a trial triggers
his daydream of standing up in court and testifying. At each stage of the story, Mitty
is forced to take the boring, monotonous details of his existence and give them symbolic
significance to enable him to embark on his flights of fancy and get the release and
freedom that he does not have in life. Thus the symbolism in this excellent short story
lies in the symbolism that Mitty gives objects and actions, such as in the last
daydream:

He
stood up against the wall of the drugstore, smoking... He put his shoulders back and his
heels together. "To hell with the handkerchief," said Walter Mitty scornfully. He took
one last drag on his cigarette and snapped it away. Then, with the faint, fleeting smile
playing about his lips, he faced the firing squad; erect and motionless, proud and
disdainful, Walter Mitty the Undefeated, inscrutable to the
last.