In "The Secret Life of Walter Mitty," what are the similarities between Mitty's real life and his daydreams?
In the short story, Walter Mitty does not actually take any direct action comparable to his daydreams. Instead, he is inspired by a general desire for adventure and danger, and the various things he sees while on his daily errands. For example, he sees a hospital, and imagines himself as a surgeon; he hears a newsboy shouting about a famous trial, and imagines himself as the defendant. Other than that, he mostly just picks up on whatever interesting things are happening in the world and fantasizes about playing a central role.
He picked up an old copy of Liberty and sank down into the chair. "Can Germany Conquer the World Through the Air?" Walter Mitty looked at the pictures of bombing planes and of ruined streets.. . . "The cannonading has got the wind up in young Raleigh, sir," said the sergeant. Captain Mitty looked up at him through tousled hair. "Get him to bed," he said wearily, "with the others. I'll fly alone."
(Thurber, "The Secret Life of Walter Mitty," bnrg.cs.berkeley.edu)
Mitty's daydreams speak to his dissatisfaction with his daily life and his ordinary problems. He has no conflict except inside his own head, and he doesn't make trouble for others. He gets flustered when people confront him, and then imagines how he might avoid the confrontation in the future instead of taking any direct action. Mitty is, in every sense, the ordinary man without ambition or drive to take risks or better himself.