The mood of a story is also called its tone, the feeling it produces in the reader. The tone of a story is determined by the author's attitude toward the characters and their situation. Does the author take them very seriously, for example, or does the author find humor in them? The tone in Thurber's story is one of gentle humor. Walter Mitty loses himself in the most thrilling, dramatic adventures, and the humor in the story is created by the contrast between Mitty's mental fantasies and his real life daily activities.
In each of his daydreams, Mitty is the hero--brave, daring, powerful, and the center of everyone's attention. This emphasizes how meek and powerless he really is, pushed around by an overbearing wife. This may make Mitty seem like a sad little man, but Thurber does not emphasize this element in the story. The humorous tone of the story is continued in its conclusion. In Mitty's last fantasy, he stands bravely before a firing squad, scorning death itself, until his wife's voice snaps him back again. The subtle (and funny) suggestion is that for Walter Mitty, facing a firing squad is preferable to dealing with Mrs. Mitty.