Villain Makes the Plot

If you study story structure, you know that stories kick off with a decisive event-- the 'inciting incident' or 'call to adventure'. This event disrupts the protagonist's status quo and spurs them to action, kicking off the rest of the plot. In other words, the antagonist is the one who starts off the story and keeps it going.

I think this is true even of stories where the protagonist seemingly initiates the adventure. For example, if a mountaineering enthusiast finally gets their chance to climb Everest, the plot doesn't start getting interesting until something goes wrong-- a storm, an evil climbing guide or what have you. Otherwise you have a piece of travel writing about someone having an uneventful (if impressive) climb. Further conflict will then stem from how the protagonist responds to those events.

In stories where there is a high degree of background discontent, such as a dystopian society or a Fantasyland nation which has recently been occupied by the Evil Overlord, there still needs to be an event which-- for the protagonist at least-- turns the unpleasant-but-bearable status quo into an untenable situation which requires their immediate reaction.