Sorry, I should have been more specific. Changing the game state by having your character do something is fine. I was talking about changing the game state from the DM's side of the table. E.g., "Suddenly, and for no apparent reason, a piece of the ceiling collapses, landing on the evil necromancer."What's the objection to the player changing the game state to gain advantage? Isn't that something that good players try and do?
(Maybe there are RPGs where that's part of game play? Could be fun. But this is the 5e forum.)
Like all these things there are gray areas in the middle, of course, and I'm sure we could both come up with examples of players narrating a change in game state for advantage that would be fine. But the existence of twilight does not disprove the difference between day and night.