I think the example was there being a secondary roll to determine the presence or absence of a complication; and if that roll were player-visible it might force the dM to add a complication (because the players would expect it due to the roll they just saw) where a complication just doesn't make sense.
I know of no system where "fail forward" is codified and could ever be used to introduce a complication that doesn't make sense. Such systems
begin from their very foundation by saying that you should do things like, as PbtA games put it, "begin and end with the fiction", for example. If something is so completely stupid, so utterly bonkers weirdo unnatural, you shouldn't ever do it. Doing so would be,
explicitly, against the rules.
In systems that lack this formalism, you almost always also lack the formal definition of fail-forward...so if you are okay with GMs exercising their individual judgment on what is or isn't okay to do in other ways, why would that judgment suddenly fail you only with this technique and nothing else?
Correct.
Incorrect. Even though I don't play it, I care about what it does because, for better or wosre, that becomes what the community comes to expect.
Which means when it does something I think is either really good or really stupid I'm gonna call it out. Same goes for 4e, or did during its day.
Fair enough--but "care" in this case is less about caring in any way whatsoever, and more about...well, what Hussar was trying to achieve with the argument given. That is, his clear goal was "you support X because it's present in D&D, so why do you have a problem with X when it comes from something not-D&D?" Hence, using an example drawn from 5e is likely to not be very convincing to you, because you could quite easily just say, "That's one of the things I think is really stupid about 5e, and one reason among many why I don't play it." The argument would be more effective, more pointed, if it were to call out a usage in a game you do play and thus, implicitly approve of, or have to justify why you
generally accept that game but reject just that one part of it.
In simpler terms: 5e doing something doesn't necessarily faze you. "Sure, it does that and I hate it." But if, say, AD&D does something--doubly so if you personally
use that mechanic, since I know you use a substantial but relatively fixed set of house-rules--that would be rather more persuasive. It would either require you to explain why AD&D's usage is good and <non-D&D game>'s usage is bad, or why you rejected that part of D&D and thus have been distancing yourself from D&D itself for some time (and thus inviting "are you actually playing D&D then?" criticisms, since folks have been rather keen to separate out "D&D" from "not-D&D" recently.)