How would one summarize all of the dreams that Walter Mitty has?
Walter Mitty's dreams are hopes that he can be successfully assertive and respected. For, in real life Walter is humiliated by his wife ("Remember to get those overshoes"), a policeman ("Pick it up, brother!), a garage attendant when Mitty cannot park easily (Leaver her sit there...I'll put her away), a store clerk as he asks for the box that says "'Puppies Bark for It'" in response to the clerk sharp question.
After taking care of all his errands, Mitty seeks refuge in a large winged armchair. But, even there he has no dignity; his wife finds him and asks "Why do you have to hide in this old chair? How did you expect me to find you?" When Mitty makes an attempt at being assertive--"I was thinking...Does it ever occur to you that I am sometimes thinking?"--his wife merely looks at him and remarks, "I'm going to take your temperature when I get home."
Like the comedian Rodney Dangerfield ("I can't get no respect" (sic)), Walter Mitty's secret life is a dream of being assertive and receiving respect.