The Fixed Point Trope in Travel Stories

This season has seen a lot of talk in the show, and i think this is a larger trope in travel stories, that there are certain fixed points in history that you just can't change. We had this episode where all these time travellers are trying to prevent world war one from happening by intervening in this one specific incident. And instead of having it be that some kind of temporal force out there that's just going to stop you, right, like that’s just going to likan tad, make you slip on the banana peel, you guys wrote it so that actually it's this white dud in a top hat who's kind of slipping in and preventing people from changing the time