That one person or two persons' inaction or actions doom the world.
I dislike this trope a lot, along with the "only the one can save the world". For me, it shows that your world is dead. If there's something more in the story, I may continue, but this alone can stop me from checking it in the first place.
In a world that is "alive", tens of organizations and hundreds, or thousands, of people would fight to prevent it. If they fail, I'm okay with that, but having the villains and heroes achieve it so easily drives me nuts. Where is the temple, the spies from other kingdoms, the government, the workers? They're non-existent.
If one of our presidents goes nuts and wants to nuke a country, there will be a ton of opposition. Because the world is "alive".
One of the stories that I can put as an example is "I'm the real one." If you want to do it, it's fine, but make sure there is a world outside of your main characters.