Narrative
Chekhov's Gun
A dramatic principle that states that every element in a story must be necessary, and irrelevant elements should be removed.
In Depth
Anton Chekhov famously wrote: 'If you say in the first chapter that there is a rifle hanging on the wall, in the second or third chapter it absolutely must go off.' It is a promise to the audience that details matter.
Example
"The subtle shot of the loose stair railing early in the movie that causes the villain to fall to his death at the end."