Now if the GM has some S in mind, and does not want to vary that, that may be the GM's prerogative (at least at some, perhaps many, tables). But a GM who does that, therefore forms the view that the player's desired outcome falls outside R(O), and therefore tells the player that their desired outcome does not come to pass is not enhancing, or increasing, or even upholding, player agency. They are exercising their own agency as author of the shared fiction. In particular, they are insisting on their own authorship of S as they have envisaged it.
This is a very GM-driven style of RPGing.