DragonTypeWyvern

Every edition since at least 3.0.

In the sections describing how skills work and what circumstances you should allow checks for them, and the sections describing bonuses to those checks, what the role of the DMs and players are, including several very specific references to how character attitudes are very important to the DCs of those checks and the fact that skills only affect those attitudes in the first place and they aren't mind control.

In other words, the whole fucking thing.

It could be, but it doesn't have to be. It all depends on the characters involved.

The DM can referee in the dispute but they (usually) can't say your character would or wouldn't believe something.

A good DM might ask you to in-character justify your bias, for example. They're also supposed to listen if you say "I don't trust Count Fuckface on account of him having a history of being a Fuckface and also he's standing over a cooling corpse with bloody hands."

If a player is metagaming that's a separate problem from their character being biased, or having a reasonably justified suspicion or whatever.

Or never, ever being interested in the creepy player's character because they don't like their vibes.

And

A

Player

Can

Decide

They

Do

Not

Care

What

The

Lie

Detector

Says

Or

How

It's

Calibrated

It's a particularly interesting example you've chosen given that lie detectors are fucking pseudoscience and a specific character might not believe one single fucking thing they say

And he can think whatever the fuck he wants about that, which is entirely my point, because he, as a theoretically sentient being, is aware that he is flawed.

Unless there's a character driven reason not to! Arrogance, naivete, backstory, whatever.

But, more pressingly, my point is to make you aware that there are more options available to the system for Deception checks than pure statblock measuring! And every table should be aware of that!

As well as the fact that Persuasion and Deception are not mind control.

Which I'm still not convinced you are, because this argument is still going.

Sure.

And you as the player are the one who decides what the metaphorical wind is like for your character's attitude towards the people and world around them.

Don't trust the king? Good news, you can tell the DM that, and they can't say "yes you do" unless you are affected by magic. They also can't roll the king's Persuasion to change your character's mind about that without you agreeing to how the DC is set, including potentially a straight contested roll.

Or, to put it another way:

Just because they didn't find a trap in the hallway doesn't mean they have to think there isn't one, especially if there's a posted sign saying "This hallway is trapped."

Yes, you are, and you don't know enough to know what you just said.

"I have a super high iron will and so I get a +40 to any mind affecting spells!"

Not what I'm saying, and I know you don't understand the problem, because you're talking about spell save DCs which are not skill checks and are specifically under DM purview as a magical mind altering effect.

Think of it like this:

You have the right, as a player, to decide your character fucking hates someone so much they will not believe a word they say under any circumstance.

That would be, in terms of interpreting that to mechanics, setting the Skill DC to "impossible." Which is ALWAYS AN OPTION FOR SKILL CHECKS. You can not jump to heaven with an Athletics check (normally speaking).

It could be you're metagaming, but that's a separate problem beyond the scope of skill, ability, and spell save checks.

The multiple sections where it says the DM doesn't control the PCs and describes the mechanics and reasons to roll skill checks in the first place.

Having a section describing how to do a contested roll isn't the same thing as saying that is how you handle all player vs player skill checks, and it assumes you know that circumstances should affect the rolls beyond the numbers on your character sheet.

Tbf 5.0 is actually pretty bad about splitting up this information between the PHB and DMG, and assuming players have a better grasp of the whole picture than it should.

For example, in that Contested Roll section, it has this paragraph:

"Both participants in a contest make ability checks appropriate to their efforts. They apply all appropriate bonuses and penalties, but instead of comparing the total to a DC, they compare the totals of their two checks. The participant with the higher check total wins the contest. That character or monster either succeeds at the action or prevents the other one from succeeding."

It assumes you know this has to be used with the sections describing things like environmental and attitude bonuses, and the sections on player agency and cooperative play, or for that matter NPC attitude tiers and how those specifically work with Deception and Persuasion, but it's easy to gloss over that line and think it simply refers to a character stat line.

It also assumes you know that rolling that as contest was an option and not a requirement in the first place.

The DM sets the mental circumstances for their characters and you set yours.

Your character is not summed in its entirety by their skill bonuses, and the DM by definition does not know your character better than the person playing them.

That character, like any other person, can refuse to believe something they don't want to believe, for whatever reason makes sense to them.

For example, they could ignore someone telling them an objective truth they could easily verify themselves by reading the relevant portion of the DMG.

Perhaps I'm wrong, but from their response and seeing this situation happen so often it sure doesn't seem like the players are aware that all skill checks have inherently circumstantial difficulties.

Simple roll vs roll contests just tend to be the default of players that haven't read the rules for these circumstances, something about the way the game is set up just doesn't clue players into that fact.

Maybe it's just that players simply aren't primed to accept that they can set their own DC bonus and it's not even metagaming? It's basically the only circumstance that they can. It's probably a good DM habit to get into, come to think. "What's your character's willingness to believe this" type prompting.

Sure, you can agree to anything.

If you didn't think it through and thus suffer from skill issues.

And there are of course good stories to tell with it, like in this secret traitor situation, and good players will apply circumstantial bonuses fairly.

Like perhaps that paladin doesn't WANT to believe their comrade is a murderer.

Doesn't mean you shouldn't be aware that another player can't force you into simple contested rolls on the nature of reality that you can't possibly contest, ever.

Hell, even if they're right! You can play a completely deluded madman that looks at a windmill, hears an NPC tell him the absolute, objective truth that it is a windmill, and decides it's a giant instead.

Wrong. For one thing, players don't have to agree to contested persuasion at all, feel free to look that up. Even if they do it's not just a simple dice contest, otherwise every face character would have free mind control over their entire party.

For example:

Player Elon Musk throws a Nazi salute. He uses his Deception +6 to claim that's not what it is, rolls a 5 for a total of 11.

Player Not A Moron rolls a 1. This does not matter, because they know what they saw, and further, they remember all that other Nazi shit he's been saying. They have effectly set their own Deception/Persuasion check DC to 30+, or roll+bonus+30 circumstance bonus.

Player Stupid Fucking Simp rolls a 20. This also does not matter because, as a stupid fucking simp, they already believe everything Elon says and take a -30 circumstantial negative and critical success skill checks are silly homebrew nonsense.

Tl;Dr you're forgetting that circumstance, including character emotions and affection, affects difficulty of all skill checks. If a player agrees to ignore that that's on them.

This also, btw, applies to NPCs trying to persuade the party. The DM does not a have a right to tell your character what they believe or disbelieve without magical effects.

If you think about it, beyond the fact of the player being the only one can say what their character is in totality and is biased towards as a result, this is how a system must work to prevent RPG horror stories of incels forcing other players into sexual or abusive situations, eg "ummm I rolled a +29 so your character has to sleep with mine and you have to roleplay it"