How does Bowker contrast courage with the reality of the setting?

Throughout The Things They Carried, O'Brien contrasts the glorified expectations of war with the grim reality. Norman Bowker's experience camping in the field beside the Song Tra Bong is no different. In the "Speaking of Courage" chapter of the novel, Bowker is home after the war, driving around a beautiful but dangerous lake, thinking about the time he "almost won the Silver Star for valor."

There are primary setting at work here is the field of excrement he and the rest of Alpha Company camped out in, the field in which Kiowa died because Bowker gave up trying to pull him out of the muck. Bowker is hung up on that moment, when he couldn't bear to keep pulling on Kiowa's arm and let go and got himself out. He says,

"Sometimes, like that night in the shit field, the difference between courage and cowardice was something small and stupid. The way the earth bubbled. And the smell."

This seems like he is making excuses for his actions, but taken in the context of O'Brien's other vignettes in the novel, it speaks to a larger theme. While Bowker's father is caught up in the idea of courage that can be measured in how many metals one earns, Bowker knows that his experience of war and courage is not so easily quantifiable:

"He wished he could have explained some of this. How he had been braver than he ever thought possible, but how he had not been so brave as he wanted to be. The distinction was important."

To Bowker, courage is only understandable in the context of the war itself. As O'Brien points out time and again, the Vietnam War was so much messier, more inexplicable, and more futile than anyone not involved could understand. All this is represented by the field and the muck and the smell of the setting where Kiowa died. Bowker feels like if he could just explain this, people would see that he was courageous, even if he was not as courageous as he wanted to be.