It’s not an undefined resolution. It’s acknowledging you can’t reasonably have rules for everything.
You cannot have
individual, singular rules for everything. Everyone leaves out that part: the idea that, if you have a different situation, you necessarily have different rules for each one. That, I completely agree, is not merely unreasonable, it's
impossible. No system of individual, singular rules could ever be totally comprehensive.
That's why you abandon the need for every situation to have a singular, individual rules expression. You embrace the fact that rules are
always abstractions, and put that abstraction to work for you. My preferred expression of that is what I call "extensible framework" rules. Skill Challenges are one example of this concept. "Montage" sequences are another. What I've heard of
Blades in the Dark's rules sounds like another example. DW's moves like Undertake a Perilous Journey, Supply, Carouse, and even basic ones like Discern Realities, Spout Lore, and Defy Danger (probably the single most commonly-used move) are all examples of extensible frameworks: using one core, abstracted structure, you can cover essentially anything within the particular scope of that move. If it makes sense as a journey from one place to another that could be dangerous and uncertain, then that move is pretty much guaranteed to work, or at least be an extremely good starting point with some minor tweaking (e.g. it's perfectly applicable for ocean voyages with light tweaking, but might need some creativity if applied to a vision-quest type "journey into the mind" thing).
I've never played Apocalypse World, how do they do it?
I haven't played AW, but I have played DW, and it's reasonably close.
Firstly, as noted above...many of the moves are abstract. This is the text of Undertake a Perilous Journey:
When you travel through hostile territory, choose one member of the party to act as trailblazer, one to scout ahead, and one to be quartermaster (the same character cannot have two jobs). If you don’t have enough party members or choose not to assign a job, treat that job as if it had rolled a 6. Each character with a job to do rolls+WIS. On a 10+ the quartermaster reduces the number of rations required by one. On a 10+ the trailblazer reduces the amount of time it takes to reach your destination (the GM will say by how much). On a 10+ the scout will spot any trouble quick enough to let you get the drop on it. On a 7–9 each roles performs their job as expected: the normal number of rations are consumed, the journey takes about as long as expected, no one gets the drop on you but you don’t get the drop on them either.
As usual, rolls are 2d6+MOD, in this case, WIS. (Three-letter abbreviations are always the modifier; if you use the full
word, it's the total score. A very nice convention.) 7-9 is partial success, 10+ is full success. The rule is pretty abstract, because all the concrete details come from whatever fiction prompted the bold trigger: travel through hostile territory. Likewise, the
reason is irrelevant; only the things needed to resolve the trigger are relevant.
DW has really excellent extensible design like this. Defy Danger is literally a single move for all possible "you're in trouble, how will you get out?" situations, be they combat, exploration, social, moral, magical, whatever, it's your one-stop-shop. That's what makes it so commonly rolled. And the results are simple. 10+, you're in the clear. 7-9, "you stumble, hesitate, or flinch: The GM will offer you a worse outcome, hard bargain, or ugly choice." Meaning, it's not a total loss...but you're scraping through, not sailing. 6-, you're gonna have a bad time. Damage, or something equally nasty (splitting the party, revealing an unwelcome truth, showing a downside to their playbook/moves/etc., or some other Bad Result).
By moving away from rules that need to give each individual situation its own singular rule, you can cover huge swathes with very few rules. The "basic" and "advanced" moves of DW, that is the generic ones any character can make use of, fit on two sides of a single sheet. And using the formats presented by those moves and others in the default playbooks, it's nearly effortless to create new moves in the same vein.
Because what bugs me is that D&D has guidance as well. What some people keep calling rule of cool is just following the rules of the game. If outcome is uncertain, make an ability check adding appropriate proficiency if applicable. Throw in advantage or disadvantage if it makes sense. Done.
I would argue that the major difference between the mere (and IMO not very good, but you already know that) guidance in 5e and the "real" (again, IMO) Rule of Cool is that the guidance there is just to make rules logjams less likely to happen; the Rule of Cool is about ensuring that what is
fun (if reasonable) does not get trumped by what is
predefined. "If it's uncertain, roll" is not at all the same as "don't say 'there's no rules for improvised flight, so you can't,' say 'let's figure out how this would work, because I love that idea and there aren't any rules covering this' instead."
