"Uncertain" can actually be very circular in this simple sentence, it could be uncertain because you have decided to use dices to resolve it, for example.
Well, no, it literally can't. It may not use the word "then", but it's an if-then sentence. If this, then that. Choosing "that" first would be to get the order incorrect and therefore would be a misuse of that rule. The circular aspect is a clue that it's not the right(RAW reading) way to do it.
Or it might be uncertain because it depends on simple circumstances, on whoever using the skill being at the top of his shape or not, of simple luck, or whether he knows (or not) that what he does is adapted (or not) to the target of the skill, etc.
Circumstantial game reasons for uncertainty will be decided BEFORE the roll happens. If there are circumstances like being beat to hell, exhausted or whatever, those are examples of things that could put a certain outcome in doubt, requiring a roll. They aren't contradictions to what I am saying or the rule in question.
It also might be linked to very "meta" considerations like whether you are Rolling with It or Ignoring the Dice (The Role of Dice), how much you believe in player agency being something inviolate, etc.
This falls into the realm of playstyle. Sure, a playstyle can alter the other rules of the game. If you are engaging the roll with it rule, it's a more specific rule than the general one requiring rolls only when the outcome is uncertain and there is a meaningful chance of failure. It specifically says to roll for just about everything, so that's what you do.
An example of specific beats general doesn't change the ability check rule into a guideline. Not that in 5e a rule isn't a guideline and a guideline isn't a rule. 5e doesn't really differentiate between the two.
And especially on this last point, which I've seen being used in this thread, I would like to remind people that it's not something that is ever used in the rulebooks themselves. The only thing there has to do with advice and table rules, nothing hard and fast. So stating that a result is not uncertain because the player will determine the result is for me a really, really REALLY strong example of the "rule" above being twisted into something that has nothing to do with the RAI, just because some people strongly believe in a principle that is far from being universal and is actually not supported by any of the rules or even guidelines.
I don't think player agency is the reason behind what we are arguing. Player agency certainly touches on it, since allowing the player to decide does give the player more agency, but it's not the motivator. The rule is the motivator.
As an side, player agency is mentioned in the DMG one time on page 241 when talking about when to award inspiration.
So no, that "rule" is actually much more of a guideline to me... Which does not mean that you are wrong, but that there are so many ways to play the game that statements like this have actually a high likelihood to be not applicable to at least some of us due to the extremely open nature of the game.
Fair enough.
