JFarrell71
SasqWatch
OK, that's interesting, I thought the DM would be more .. rigid about it, and would rather prepare the same surprises in the conversations so that you wouldn't necessarily know whether skills should be boosted or not. Unless you asked questions before the dialogue, to get some hints.
A GM is under no obligation to make every solution work, but they shouldn't outright reject a valid attempt.
Like in my example from above, a GM could assign a very high DC to that bluff attempt. Or they could even decide that the guards all know each other in their very elite unit and that there was no way a bluff could EVER work….but what a GM shouldn't/couldn't do is flat out tell the player they can't try to bluff. (A good GM would probably ask for an insight roll, and if successful, warn the player about their imminent failure). You can try to tell your mom that you didn't eat the cookies while crumbs fall off your lips, even though it's never going to work.
It's like that for any valid action in the rules. The GM doesn't arbitrarily pick and choose which valid skills, spells, etc the player can use in a particular situation. But they very much can adjudicate how those attempts work out. In a computer game, because every response has to be anticpated and coded, the developers DO have to pick and choose which things can be used in a particular situation.