“The Shape of the Sword” or “The Form of the Sword” (“La forma de la espada”), by Jorge Luis Borges
Wikipedia says this first appeared in La Nación in July 1942 and was collected in Ficciones in 1944; found Donald A. Yates’ translation here
1,906 words in the translation linked above
One thing that impresses me about Borges, again and again, is the psychological astuteness that shines through his best intellectual games:
“Then I realized that his cowardice was incurable. I begged him, rather awkwardly, to take care of himself, and left. I was ashamed of this frightened man, as if I were the coward, and not Vincent Moon. One man’s deeds are like the deeds of all mankind. This is why it is not unfair that one disobedience in a garden should contaminate the human race; this is why the crucifixion of a single Jew should suffice to save it. Perhaps Schopenhauer is right: I am others, any man is all men. Shakespeare is, in some way, the miserable John Vincent Moon.” (From another translation; quote found online here.)
The philosophical tangent arises naturally from the character’s feelings.
When I first reached the ending, I felt for a moment that the scene quoted above had lost its charm for me. It had become too literal, Moon’s sense of the blurring of identities seemed less meaningful, and it made Moon as narrator seem more calculating. But on reflection I see that the ending merely rewrites that scene. Now the scene is no longer about Moon’s companion feeling vicarious shame. It’s about Moon sensing his companion’s awkwardness and understanding exactly what lies behind it.