Walter Mitty's wife is an emasculating and meancing presence: She dictates to him what he must do and stifles his masculine sense of adventure. This repression is what causes Mitty to daydream; his dreams create heroism and leadership.
Mitty must drive with his wife to the city for the weekly shopping, etc. When they first arrive in town and Mrs. Mitty gets out to get her hair done, she tells her husband to get overshoes. Mitty retorts, "I don't need overshoes," but she patronizes him as one would a child: "We've been all through that...."
As compensation for his lack of masculine assertiveness, Mitty's first daydream is that of his being a famous surgeon who "saves the day." Later, he imagines himself a bombardier, a hero. Yet, in reality he cannot change the chains on his tires in winter, and despite his attempts at defiance, he acquiesces to his wife's menacing orders and retreats again and again into daydreams in order to escape his overbearing wife.
Mitty is a daydreamer whose wife treats him more like a child than a husband. This is because Mitty is immature and tends to escape into his daydreams rather than deal with reality. So his wife dominates him. She nags him about everything but if she was not so controlling, Walter would be lost in his dreams. She is his link to real life. She prevents accidents from occurring when Walter daydreams and loses track of where he is and she keeps him from losing total contact with reality.It seems they need one another. His wife needs someone to control and Walter needs a person who can control him.
Mitty's wife does seem to get after him quite a bit, but at least she cares about him. Mitty's daydreams are not healthy in that he is is disconnected from the real world a little too much. Today, someone would think he had Alzheimer's.