In this short story, the context is obviously the Vietnam war in the 1960s. The tale consists of the thoughts of Lieutenant Jimmy Cross as he leads his men and also simultaneously day dreams of a girl back home, Martha, a student who is back in the States. However, as a result of the death of one of his men whilst he was daydreaming about her, Jimmy Cross burns her letters and photo and determines to have "no more fantasies." Note his reasoning for this action:
Henceforth, when he thought about Martha, it would be only to think that she belonged elsewhere. He would shut down the daydreams. This was not Mount Sebastian, it was another world, where there were no pretty poems or midterm exams, a place where men died because of carelessness and gross stupidity. Kiowa was right. Boom-down, and you were dead, never partly dead.
The context is so important in this short story because O'Brien shows how the grim realities of the war effectively end the youthful innocence of Jimmy Cross as he forces himself to shut down his emotions and thinks that in war his leadership of his men means that there is no room for daydreams, even though this is shown to be a necessary ingredient to help him survive the onslaught of the realities of war. What grounds this story in its context is therefore repeated reference to the Vietnam war and the very frightening realities of what that meant for the young American soldiers that fought in this battle.