Chaosmancer
Legend
This is only partly true. While the DM can call for a contest of Charisma (Deception) and Wisdom (Insight) checks to resolve these sorts of tasks (when said tasks have uncertain outcomes and meaningful consequences for failure), a contest is not required by the rules. The DM can instead just set a DC.
This is like saying Perception isn't used to oppose Stealth because the DM can just set a flat DC.
Technically true, but talking beside the point instead of addressing it. When an opposed deception roll is used, it is default of Deception vs Insight.
What you're missing is that the DM decides if there's ambiguity in the result. If the DM simply decides that the lie (or any other insight) can't be detected, or that the way the player proposes to accomplish it would automatically fail, then there's no roll. Thus the absence of the roll should not be a signal to the player that the NPC is telling the truth.
Now, I think DMs should be very sparing with completely undetectable lies (maybe if it's a construct doing the lying or something), but the point is that just because a player proposes a course of action...or wants to "use a skill"...it doesn't entitle him/her to a roll. Which in some ways is the heart of this whole debate.
I think most players would realize the situation where Insight is impossible. Such as trying to Insight a recording or a letter.
But, to get to a question that might have an answer. If they tried, and there was no ambiguity because it is too easy. What do you tell them?
Do you tell them no roll is necessary and just leave it at that, or do you tell them that no roll is necessary because they can easily tell?
I've had times I've needed to tell players "No, the letter isn't lying to you" when they try and use Insight in a manner where it does not apply, but I let them know why there isn't a roll necessary, which means they either know it is impossible to tell or they succeed. And succeeding by realizing it is impossible is... kind of weird.
.Full stop, right here. The player has stated an action with a goal and approach, the GM is now obligated to narrate the results of that action. If the GM decides there's no uncertainty, the GM still must narrate the outcome.
See, I think you stopped the conversation too late.
Player: "I don't believe him, I think he's hiding something."
DM: "Okay."
Player: "Umm...can I get a read on him? An insight check?"
DM: "No."
Player: "What do you mean?"
DM: "The players don't get to ask to do skill checks. They declare action and intent."
This would get me frustrated. It reads like a "power play" on the part of the DM. They want to force me to say things in a certain way
Ok...ehem...I'm at a keyboard. Here's my understanding of the "it's all about character skill" approach:
DM: "In front of you is a door, looks like oak with metal strap hinges, riveted on. There's a pull ring in the center."
Rogue: "Hmmm...we found that poison lab. I'm going to carefully inspect that pull ring to see if there's any foreign substance on it. I'll look from different angles, and maybe sniff the air. Oh, and I'll cut off a piece of that cultist cloak I found and carefully wipe the pull ring to see if anything comes off. I have proficiency in Poisoner's Kit so I should know how to do this safely."
DM: "Roll Investigation."
Rogue: "Hmm...11."
DM: "Nope, seems clean."
Rogue: "Ok, I'm going to pull the door open."
DM: "It has contact poison on it; roll a save versus Constitution."
Rogue: "What? I looked for contact poison!"
DM: "Yeah but the DC was 12; you just missed."
Rogue: "Wait a sec...it was only a 12 DC, but an 8th level rogue with Poisoner's Kit proficiency specifically looking for contact poison in the right place didn't find it?"
DM: "Not if you fail the roll. Maybe you looked on the wrong part of the pull ring."
I know this is sarcasm, and it is quite well done too, but it does lead me to a good point on DM presentation.
For an 8th level rogue with prof to get an 11... they had to roll low. Player knows it, I know it. So, while narrating the result I don't say "No you failed" I'd say something more like "You're tired of this dungeon, and while you put in a good show of looking you only really glance at the handle while thinking about the fat piles of loot in your future."
We relied on the dice, and the dice tell us the rogue under-performed. So I come up with the reason why they lapsed in that moment.
Now, I also wouldn't have gotten to that point, because they said "I wipe it with a cloth" and action no player of mine has ever thought of, and that would wipe the poison off onto the cloth. And, since this poison was potent enough to work even if the player is wearing gloves or gauntlets (yeah, contact poison handles actually would rarely work, because most people would be wearing leather gloves) then they get the check then. Or, they find the poison and no check is needed to know the handle had poison on it.