Rule of Three
A plot device in a story should be referenced three times. First is the setup, where the mechanic is introduced. Then there is a reminder of the mechanic, so that the audience doesn't forget about it. Lastly the mechanic is used, called the payoff.
This structure helps audience members feel like mechanics were an existing part of the world, rather than a cheap plot device. Often these mechanics are something that the characters should already be familiar with.
See [[Spaced Repetition]].