This story vascillates between the everyday humdrum life of Water Mitty, the hen-pecked husband sterotype, and the extravagant adventures he lives in his daydreams. Mitty flits in and out of reality, his daydreams concocted by a stream of consciousness association triggered by the sputtering of his car's exhaust pipe, a pair of gloves, and finally a freshly lit cigarette. In such a way this docile "hubby" gets to be the captain of an icebreaker, a famous surgeon, a defendent in a murder trial and finally a fighter pilot taken captive distaining a firing squad. Mitty's imagination is his "second life," which nurtures his deflated ego and helps hims escape the insufferable mediocrity of his existence.
If you do a graph of the plot line of this story, it would look very much like a cardiograph printout, with the steady horizontal line of Mitty's real life intermittantly broken by the highs and lows of his "virtual" existence.