What point might bierce be making about heroism, the realities of war, the dangers of fantasy?

In our fantasy, we tend to played out how we would always came out on top and how everything work out in our favor, and many soldiers who came into war had this exact type of thinking in their mind.
The harsh reality of war that they face would turn their stomachs. They would witness many of their close friends shot or blown up like a piece of meat and they would be surprised on the darkness that they had inside themselves from all of the killings.