Remember Show and Tell from Elementary School? It wasn’t Show versus Tell, or Show instead of Tell, it was Show and Tell.
Show, don’t Tell, is what the writer is continually told, and this is good advice . . . usually. Do not tell us your character is afraid; show us his fear.
As P. Bradley Robb says, every rule has an exception. Knowing when to show and when to tell is the sign of a writer who has learned her craft, of a writer who has found his voice.
One instance telling makes sense is when showing will slow down the pace when it is appropriate to speed it along. It always takes more time, more words to show a thing than to tell it. Sometimes showing can get wrapped up in unnecessary detail, relating a writer’s knowledge, knowledge that is not necessary to the plot, the scene or the character.
Another would be filling in background information, description or events that are not as important as scenes that you want to stand out, those which you will show.
It is always a case of: Is this scene, description, character trait important enough that it must be shown? How will showing affect the tension and pace of the story? If important showing slows down the pace too much, perhaps it is misplaced.
Back to my own novel now — hope I have shown everything at the right time and place.