So I've had a very busy day and am way behind, but wanted to respond to some of the below posts. Hopefully, they help clarify my view of the example I gave.
I don't have a problem with the DM's decision to have the Dukes men surround the barn (or at least attempt to). That seems like a legitimate consequence of the PC's holing up in a barn for the night. The whole D&D playloop of PC action, DM narrates outcomes.
What specifically is the Duke's men surrounding the barn a consequence of? That's my issue. It's a consequence, for sure, but of what I have no idea. No perception rolls or anything of the sort were called for.
The problem I do have is not even giving the lookout a perception check to notice something amiss (I'm assuming this wasn't handled by a secret stealth vs passive perception roll or something similar which is always a possibility in D&D).
No, there were no rolls made, no explanations given (either in narration or in the after play discussion). It simply happened.
So to answer the question in simple terms - it's made up, much the same way when a player in blades in the dark rolls a 1-3 and the DM gets to make up one of many plausible consequences for them.
No, there's a huge and obvious difference. The roll of a 1-3 triggers the GM narrating some bad consequence. He can't do so otherwise.
There is no obliging. The rules of the basic playloop allow this.
Then I think that's part of the problem. This is what I meant when I said the 5E structure is susceptible to this kind of thing.
Please tell me how having the PC's stay safely in the barn all night long and getting to benefit from a long rest (in D&D that's a big deal) - how didn't that honor the ability?
Please tell me how having the Duke's men surround the barn is a consequence of the use of the Rustic Hospitality ability?
The answer is that it's not. It should have been a consequence of other actions that never happened.
I'll answer. That's not against the 5e play loop. It would be against the stealth rules though.
The conflict in this statement is part of the problem.
IMO, it's because you keep on claiming that's an example of Mother May I. No one is justifying the bad DM call there - they've been pinpointing where it was and saying that's not a Mother May I example after doing so. Just to be clear, the bad DM call was in not honoring the lookout that the players left.
Because our goal was to avoid a fight with the Duke's men, who we knew were approaching town. How could we avoid a fight? I offered a reasonable means to do so. The GM decided it was not enough.
What may have been enough? I don't know. That may be the distinction you're looking for between Railroading and MMI, though I think it's hard to tell the difference given that we can't say if there was some magic way to ask to avoid the fight that would have worked.
The PCs were among commoners. They did not show themselves to be a danger to them. But the GM decided that the commoners didn't shield the PCs from the soldiers searching for them, and then retroactively established some fiction in their mind that produced that outcome (I don't think @hawkeyefan has told us exactly what that fiction was, and I don't know if the GM told hawkeyefan - but we might assume the fiction is standover tactics from the soldiers, or a snitch among the commoners.)
No, there was no indication that the Duke's men knew we were in town, or that the farmer or the other couple of people we interacted with thought we were a danger to them (they were in fact, very enamored with us). When I asked him about it after play, he didn't elaborate in what led to our discovery other than, as I said, he thought it would be cool to have the barn surrounded and burning for a cool encounter like Young Guns. I didn't press him on it to see if in his mind we were snitched on or seen by the soldiers or what. I don't think he really gave it much thought to have a specific reason.
To respond to FrogReaver, I refer to "retroactively" because @hawkeyefan has told us as much: the GM wanted a Young Guns-style showdown, and so set one up. To the best of my knowledge of this episode, he didn't even share with the players what events occurred in his imagination to bring things to such a state ( @hawkeyefan will correct me if I'm wrong about this).
Exactly right.
This seems to come back to an argument @overgeeked was making. If accurate, the player asked for an outcome. They wanted the result of their feature use to be that battle was avoided.
Sort of. More that we decided we didn't want to fight the Duke's men. The reason for this (despite D&Desque murder-hoboism) we didn't want to kill a bunch of soldiers who were just doing what they thought were their jobs. We also (again, bucking the trends of D&D) didn't typically want to fight unless there was no other option. We did consider fighting them, but the negatives seemed to outweigh the positives.
So yes, that was the goal. Then I suggested my use of Rustic Hospitality to safely hide, which we hoped would achieve the goal.
Now, to be clear, I didn't necessarily expect that this ability alone would be enough to get the whole job done, so to speak. The Duke's men weren't there specifically for our characters, but they knew who we were, and the Duke hated us, so if we ran into the, there'd be an issue. So I figured we'd need to make a roll or two to hide safely in the barn. Or that the GM would narrate some additional scenes and prompt some actions, and depending on how those went, we may find ourselves in trouble.
So it's not that I expected the Rustic Hospitality was a magic bullet for the situation that got denied. It's that it was seen as the only action that mattered, and then nothing else was used to determine the outcome.