"A Mystery of Heroism" is set against the backdrop of the Civil War. Collins, the protagonist, is a member of A Company, which is pinned down on the side of a hill by the relentless onslaught of an enemy battery. Although he's in the midst of horrific carnage, the sight of a well across the meadow suddenly fills the young soldier with a desire for a drink of water. When he expresses this desire to go to the well aloud, his fellow soldiers deride the notion that anyone would risk their lives so lightly, but hand him their canteens after he requests permission from his commanding officers to do so.
Once he begins to cross the meadow toward the well, with bullets and artillery shells whizzing past his head, he is disappointed to discover that, although viewed from the outside his action might appear to be heroic, he still feels like an ordinary man.
He wondered why he did not feel some keen agony of fear cutting his sense like a knife. He wondered at this, because human expression had said loudly for centuries that men should feel afraid of certain things, and that all men who did not feel this fear were phenomena -- heroes.
No, it could not be true. He was not a hero. Heros had no shames in their lives....
He saw that, in this matter of the well, the canteens, the shells, he was an intruder in the land of fine deeds.
So, despite an outwardly heroic deed, Collins was an ordinary man in his residual awareness of his flawed and finite nature.