The setting of the short story "Dusk" is Edwardian London; specifically, Hyde Park. When is starts to get dark, the protagonist Norman Gortsby likes nothing more than to sit on a bench and watch those around him, those sad, defeated souls who seem to emerge at this time of day.
Gortsby's detached perspective gives him a smug sense of superiority over those less fortunate than himself. But it's a very limited perspective, one that is ably symbolized by the onset of darkness. Gortsby seems to think he's a light in that darkness, yet as he eventually discovers to his cost, he belongs as much to the gathering twilight as any of the massed ranks of the defeated.
Gortsby's in the dark, both literally and metaphorically. He prides himself on being a man of the world, as someone who knows when he's being played for a sucker. Yet that's precisely what happens to him when a young con-man manages to wheedle some money out of him. After Gortsby returns to his bench and sees an old man looking about for the cake of soap that he's just given to the con-artist, he finally becomes one of those countless men and women who have "fought and lost."