Every DM has been there.
The session is going along smoothly, important plot points are being hit, then out of nowhere a player (usually a Rogue, or a Bard, though can be anyone, really) asks to do something next to impossible.
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“I want to seduce the king.”
“I want to try to kick down the magically locked steel door.”
“I pretend to be the shopkeeper’s wife.”
And, given that D&D is all about creativity and collaborative storytelling, most DMs try their best not to say an outright “no” to an eager, excited player.
So they ask that player to roll for it, or even to roll with disadvantage, figuring they’ll get something low (or at least not all that high) and the DM will be justified in having the Dice Gods say no to the player in their stead.
And then that player rolls a nat 20.
The table erupts.
And now the DM is expected to allow the impossible to happen.
What now?
Critical successes on ability checks
A natural 20 is a big deal in D&D. According to Rules as Written, rolling a 20 on an attack roll offers a serious damage boost, and landing a nat 20 on a death saving throw pops you back up with 1 hp.
So it would make sense that the results would be similar for ability checks, right?
Well, that’s where things get a little complicated.
Nothing is explicated stated in the Player’s Handbook about how critical successes or failures may come into play for ability checks. Instead, the Rules as Written state that:
An ability check tests a character’s or monster’s innate talent and training in an effort to overcome a challenge. The DM calls for an ability check when a character or monster attempts an action (other than an attack) that has a chance of failure. When the outcome is uncertain, the dice determine the results.
For every ability check, the DM decides which of the six abilities is relevant to the task at hand and the difficulty of the task, represented by a Difficulty Class. The more difficult a task, the higher its DC. The Typical Difficulty Classes table shows the most common DCs.
It also provides a task difficulty to DC table.
Very easy: DC 5
Easy: DC 10
Medium: DC 15
Hard: DC 20
Very Hard: DC 25
Nearly Impossible: DC 30
To make an ability check, roll a d20 and add the relevant ability modifier. As with other d20 rolls, apply bonuses and penalties, and compare the total to the DC. If the total equals or exceeds the DC, the ability check is a success — the creature overcomes the challenge at hand. Otherwise, it’s a failure, which means the character or monster makes no progress toward the objective or makes progress combined with a setback determined by the DM.
So say that the Bard has a Persuasion bonus of +8. Even if they were to roll a 20 on the dice, they would still only land at 28 — two short of what RAW states as Nearly Impossible, which may be what the DM considers “seducing the king” (or the dragon, or Asmodeus) to be.
Given that the official rules don’t give any sort of a special bonus to a natural 20 on an ability check like they do for attack rolls or death saving throws, then the roll merely equals 20 — which is good, but might not be good enough depending on bonuses and the set DC.
Player expectations
So let’s say in this example that the DM sees the Bard get a 28 Persuasion. The table is on the edge of their seats, expecting the king to fall head over heels for their charming Bard. Instead, the DM says something along the lines of: “Hmmm. You flatter me, and are quite charming, but I am a happily married man. Besides, a king simply cannot go galivanting with an adventurer — no matter how alluring the prospect may be.”
The players seem let down, and the Bard says that it’s unfair that he didn’t manage to do what he set out to do, seeing as he rolled as high as he possibly could.
Someone else asks the DM why they would bother to ask for a roll if there was no possible way of actually starting a love affair with the king.
Here’s the thing, though; it is the DMs job to determine how NPCs — and the entire world, for that matter — react to the PCs. Just because a player takes an action with the intention of a specific result, doesn’t mean that result will surely happen on a success, it merely means that they did the best possible job in their attempt.
Some might even consider the fact that the Bard didn’t get their head chopped off for boldly coming onto the king to be a “success” in itself.
Still, many players will feel cheated out of an epic moment if you water down their nat 20 success, so DMs should probably specify how they rule critical successes and failures on ability checks during session 0.
Natural 1s
Just as Nat 20s aren’t inherently successful, neither are nat 20s “critical fails” on ability checks — at least as far as RAW goes.
Say that same Bard were attempting to play their instrument for the local tavern. They have a Performance bonus of +10 (because Bards), but as they get up onto the stage and pull out their fiddle, the player rolls a nat 1.
They groan, thinking that they’ve royally screwed up. Maybe the fiddle’s string breaks, or the crowd starts laughing at how bad they’re playing… but the DM instead says that they put on a decent show. No one gets up to dance or anything, but there is a modest applause at the end and a few coppers are tipped.
“But I rolled a nat 1?” The bard might ask.
“Yeah, but you still got an 11, which is decent,” the DM replies.
And it makes logical sense, too, that someone who is essentially a professional musician wouldn’t ever be terrible at playing music for a crowd, even on their worst day.
The same goes for that Barbarian who rolls a nat 1 on a contest of strength, or a Rogue who rolls a 1 to hide. So long as their bonuses are high enough, they can still accomplish very easy feats within their specialized skills.
Homebrew
Now, I should make it clear that I’m not out here trying to tell anyone how they should be playing D&D — I’m just trying to clarify how Rules as Written work regarding this mechanic, because I’ve seen far too many players and DMs alike mistakenly conflate a nat 1 or nat 20 ability check to mean absolute success or absolute failure.
And given that this is D&D, you have every right to play your game that way by making it something of a homebrew rule.
Hell, it would lead to some exciting moments, after all. The Rogue trying to hide like Drax, the Barbarian being bested by some commoner in an arm wrestle, or the Bard starting a fiery romance with a king do make for memorable sessions — but whether or not these things are actual possibilities depends entirely on just how wild your DM (and table) is willing to go.
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