How does the ordering of the dreams in the story The secret life of Walter Mitty lead to a humorously climactic effect?

One outstanding feature of the sequence is that the dreams become steadily more desperate and violent. Mitty is at first a pilot and then a doctor. In the third dream, set in the courtroom, he suggests the possibility that he shot another man and then cracks the District Attorney on the jaw. In the wartime sequence, he flies a bomber. Finally, he is about to be executed by a firing squad. Perhaps the sequence suggests Mitty's increasing boredom and frustration in real life; his fantasies must become steadily more dangerous and exciting to satisfy him. Given that the fantasies are progressively more removed from Mitty's real life, there is a humorously climactic effect. The last fantasy shows him departing, literally, from real life altogether.

-From the online text book not me