The Hidden Pitfall of a Silly Mechanic

I'm going to take a quick break from the Writing Action thing to bring up something I ran into on Youtube the other day, that I never really thought of before which was the problem that can arise when you make up a rule for the universe of your story that works on a small scale, but looks ridiculous when your story calls for you to use that "rule" many times in a row.

Case in point.  In the Twilight storyverse, you kill a vampire by tearing his head off and setting him on fire. I'm kind of a vampire lore purist, but in the first book when they kill the one vampire that's stalking Bella, it's pretty straight forwards. Tear his head off, burn his body, he's dead. Fast forwards a few years to the last book and the Big Vampire Clan Battle (with special guest Big Wolves).

I've never seen so many people get their heads pulled off in my life.
In  games, they call these "universe rules" a mechanic. In chess you eliminate pieces by capturing(moving your piece onto their square) You win by trapping the king to where he is under threat and can't move out of threat. The mechanic works no matter how many times you do it in a row. Play a hundred games in a row and there is never the sense that this is getting ridiculous. Not so much with decapitation.

I guess the object lesson is when you're creating a fictional world, look into the future and imagine you story was wildly successful and what might come of that. Make sure the rules of your world can scale up.