In what way does Mitty's last daydream of an apt comment on his fate in real life?

Walter Mitty's last daydream is of his bravely facing the firing squad. He scorns the blindfold, takes a last drag on his cigarette, and bears his breast to the bullets.

Prior to this, Walter had been sitting in an old chair, waiting for his wife, and imagining himself a fighter pilot, bravely facing the enemy. The enemy, as always, is in some way symbolic of his wife. She finds him in the chair, after claiming to have searched all over for him, like a forward observer tracking the enemy. She berates him for not being where he was supposed to be, not doing what he was supposed to do, and in fact doing nothing. When asked what he had actually been doing to cause her such effort, he replies, "I was thinking. Does it ever occur to you that I am sometimes thinking?"  This bravery is met with a vicious, "I'm going to take your temperature when we get home, " which he views as approaching death.

This last daydream epitomizes his life in that he bravely faces the unhappy circumstances of his existence, knowing that escape is impossible. Thus he accepts it for what it is, though he escapes through his imagination. Though he imagines himself facing the firing squad without the blindfold, he does in fact refuse to look at his life for what it is. He is passive, as if he is facing a firing squad, with no effort to change his circumstances or confront his wife and thus improve the quality of his existence. His "death" is thus a symbol of his failure to choose his own path, but to submit to the path chosen for him by others, specifically his wife.