“Show don’t tell” is another of those writerly advice aphorisms that people refer to all the time, without really knowing the original context.
It is most often attributed to Anton Chekov as
Don’t tell me the moon is shining; show me the glint of light on broken glass.
There’s no definitive source for that, but it appears to have been derived from a letter Chekov wrote to his brother in which he said:
In descriptions of Nature one must seize on small details, grouping them so that when the reader closes his eyes he gets a picture. For instance, you’ll have a moonlit night if you write that on the mill dam a piece of glass from a broken bottle glittered like a bright little star, and that the black shadow of a dog or a wolf rolled past like a ball.
In other words, Checkov is advising writers to avoid excessive naked statements like “the moon was out” in favor of metaphor and simile.
This doesn’t mean resorting to purple prose or generating writerly prose darlings that you must later murder.
It means writing rhetorically. It means using the breadth and width of a writer’s toolbox. You can look at a writer like Hemingway and see him using the same tools. Here’s the opening of “Hills Like White Elephants.”
The hills across the valley of the Ebro were long and white. On this side there was no shade and no trees and the station was between two lines of rails in the sun. Close against the side of the station there was the warm shadow of the building and a curtain, made of strings of bamboo beads, hung across the open door into the bar, to keep out flies. The American and the girl with him sat at a table in the shade, outside the building. It was very hot and the express from Barcelona would come in forty minutes. It stopped at this junction for two minutes and went to Madrid.
Now, people look at this initial paragraph and say “Look ! He’s telling!” which on the face of it, Hemingway is. He’s giving flat, detailed assertions. But he’s also using metaphor. The next paragraph is a truncated conversation. All dialog, as they order drinks and squabble.
If you read though, past the opening and the start of the squabble, you realize that that initial scenic “telling” is mostly about the fact that the couple in the story are at a junction, just like the train with its two minute stop before going to Madrid.
She is pregnant. They are discussing an abortion. The sole specific reference to the abortion is in this dialog:
“It’s really an awfully simple operation, Jig,” the man said. “It’s not really an operation at all.”
The girl looked at the ground the table legs rested on.
“I know you wouldn’t mind it, Jig. It’s really not anything. It’s just to let the air in.”
But even here, with this direct assertions—“It’s just to let the air in”—Hemingway is in fact showing not telling, if you read closely, and think about what the dialog tells you about the speakers.