In order to begin to address this question, we must first ascertain what is the "most compelling" aspect of the story. In my opinion, there are two distinct options: first, the reason why Lieutenant Brayle was so "vain of his courage" that he would imperil himself time after time in...
In order to begin to address this question, we must first ascertain what is the "most compelling" aspect of the story. In my opinion, there are two distinct options: first, the reason why Lieutenant Brayle was so "vain of his courage" that he would imperil himself time after time in battle by refusing to take cover and second, the reason why, after going through such trouble to return her letter to her, the narrator lies to Marian Mendenhall about how Lieutenant Brayle died.
Once you have decided what you feel to be the most compelling aspect of the story (one of the two I have outlined above or something else entirely), you will need to formulate a claim—a statement that someone could argue—about that element. For example, taking the second option I discussed above, you might argue that the narrator lies to Miss Mendenhall because he blames her for Lieutenant Brayle's death. In his narration, he calls her a "detestable creature," probably because of her letter, which unequivocally states that she "could bear to hear of [her] soldier lover's death, but not of his cowardice."
It was this statement, contained in a letter that Lieutenant Brayle carried with him—in fact, he died with it on his person—that compelled him to act with more concern for his dignity than his life. Then, Miss Mendenhall, who essentially condemned Brayle to death, casts the letter into the fire when she learns that the stain on it is his blood. She seems to have no sense that his death is really on her hands, and she has an incredibly shallow, prissy response to his death. She does not even show any grief. Finally, the narrator implies that Miss Mendenhall is a snake when he tells her that Brayle died when he was "bitten by a snake" rather than the truth: that he died in battle. Instead of blaming Brayle himself or the soldiers who shot him, the narrator seems to blame Miss Mendenhall, and all of these factors help explain why he lies to her. She does not deserve to know the truth or to have the satisfaction that it would, evidently, bring her.