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Just Deus Exit Machina and Forgotten Phlebotinum
We can never truly eradicate the coronavirus, but we can suppress its threat like influenza
Found it! Was pretty close with the name too: Broken Story Breaker
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This would be Holding Back the Phlebotinum
The ones 4tellolife4 mentionioned, Plot-Driven Breakdown, and It Only Works Once are specific ways to "break" the dangerous power/item.
^ does that cover "destroyed phlebotinum/device/weapon" too?
If yes, then we don't need that draft
We can never truly eradicate the coronavirus, but we can suppress its threat like influenza
^ Yep. Covers any situation where "even though we did this before we can't do it now"- even calls out No Plans, No Prototype, No Backup as a common Hand Wave for it.
There was a trope in TLP that I'm not sure ever launched where a powerful item in a work is destroyed so it won't later break the plot of the work. Was that ever launched?