So, we had ended last session of our Shadow of Yesterday campaign on a cliffhanger: the villain, tied and captured, spells a Zu sentence (a powerful form of magic), but when we played next time and I detailed the scene (the Zu sentence itself), I rolled on the villain's behalf, only to find that he failed miserably, in a sense, ruining the high note I kind-of-hoped to kickstart the session.
So, what happened, I think? As a GM, NPCs are the tools I use to push players or to demand action from them, so having to filter my "move" through a roll kind of blew up the situation players would react to. I think this is a strong point of games where the NPCs don't roll dice and your input manifests directly as a change to the situation.
Additionally, this roll prompted a question by one of the players: how does failure manifest for Zu, which odd effect does this magic school have, when you fail? This created another misconception, in the sense that failure in that game, for me, is a tool you use to transform the player's input into something different, not necessarily something you apply to your own input.
This got me thinking about replacing npc rolls, next session, for a static result.