1. A gimmick or storyline may be reused freely and safely after a few years of dormancy.
2. The unwritten rule that, after a given number of years, there has been enough turnover in the fanbase that a writer can re-use the same gimmicks and storylines with impunity.
The fleeting demographic rule allows YouTubers to reuse jokes and catchphrases after they have become repetitive.
The act of tapping a bong, pipe, or rig 3 times with a lighter before the first hit, as a smoking ritual among common stoners to strategically move the ash for more air flow.