Whose theory?Yet in the Duchess example the fictional content you're trying to influence is the roleplaying of an NPC - which in theory is supposed to be GM territory.
That's the whole point of my post, which is an elaboration of one aspect of what (I take it to be that) [MENTION=5142]Aldarc[/MENTION] is saying. Some people like to play a RPG in which the GM decides everything that happens except (perhaps, if there is no fudging of the combat rules) who gets beaten in fights. Others don't. And it's hardly a new idea. I already cited Classic Traveller which has rules which allow the players to declare actions which result in NPCs acting one way or another. Moldvay Basic also includes reaction rules, and examples of the players declaring actions which are intended - as mediated by those reaction rules - to determine the behaviour of NPCs (some hobgoblins).
Both Classic Traveller and Moldvay Basic also have morale rules, which are another set of mechanics for determining NPC behaviour.
As a general rule it is the purview of the GM in the same way that it is the purview of the GM to decide what a NPC does in combat.do you agree or disagree that the roleplaying of NPCs is the purview of the GM?
But if a NPC is dead, the GM is bound by that. If a NPC is subject to a Suggestion spell, the GM is bound by that. If a NPC is persuaded by a PC, the GM is bound by that.
The whole function of mechanics is to constrain, and establish, the content of the shared fiction.
What do you mean by "the odds" here?If the PCs want any hope of success beyond simple random chance they need to do both: get what info they can and then roleplay their interaction with the NPC(s) using that info where and how it best fits in order to sway the odds in their favour.