There’s a scene in the Great Muppet Caper, in which Lady Holiday explains to Miss Piggy the backstory for the entire movie.
Miss Piggy: Why are you telling me all this?
Lady Holiday: It’s plot exposition. It has to go somewhere.
The Muppets are a classic in my family, and whenever we catch serious movies forcing blocks of plot exposition into dialogue for convenience, we roll our eyes at each other and quote Lady Holiday.
It’s a good rule of thumb to make sure you Show Don’t Tell by giving everything you write the “how can I translate this to the big screen?” test, but shoving all your plot into dialogue and all your character development into voiceover is cheating – and it will show in your work. Perhaps a better way to remember the rule is “Imply, don’t state.” Let’s switch to an example of Imply Don’t State done right in a movie.
The Book of Eli opens up in a forest, gray with fog, where lies a decaying human body. A skin-and-bones cat is picking at the carcass. A few feet away, a hunter waits, aiming a crossbow. He sees the perfect moment, shoots the cat, picks up the dead creature for his next meal, and leaves the human body.
This seemingly simple first scene conveys everything we need to know in one fell swoop. Something terrible has happened in this world. Times are desperate. And even though we don’t yet know the main character’s name, or where he comes from, or where he is going, we know he won’t eat human flesh, even if he is starving. He also doesn’t bury the body, but thanks to the previous fact, we know this is not due to a lack of respect for human life. Either he’s seen too many human bodies to bother burying one of them, or he has more important things to do. Or both. We also know that he has patience and skill with a weapon.
We learn all this in less than five minutes, without hearing a word of dialogue. And it’s brilliant. Approach your novel (or short story) the same way.