Having the bad guys never do those things would feel strange. Having them always do it gets like the shows or comics where the villain always monologues just enough for the hero to be rescued. Once in a while the monologue is worthwhile, the rest it just feels like it's rubbing my face in how the risk wasn't real. Maybe this is why I loathe comic stories where failure is the world being destroyed. You know if it does happen time travel or some other cheese will fix it... (which was fine the first three times I read it).
As with many things, judicious use matters. I told my players the game I run is overall bright. Enemies prefer to take prisoners because they consider prisoners useful, for ransom, conversion, sacrifice...various benefits.
Most won't totally fight to the death, but some will because they have ideological commitments. Etc.
As for the other bit there, IMO a story which hinges
only on the final outcome being totally uncertain is not very effective as a story. It is better, more effective, to make a story where the outcome is less relevant than the journey. If the world is in danger, if
will be saved, but what will the characters
sacrifice in order to save it? What hardships will they endure? How will they fundamentally change as people because of that story? That's where the actual drama and meaning lie.
Final stakes are less effective than
ongoing stakes unless a story is genuinely about to end...and even then, most times, failure at the end would be a deeply unsatisfying ending. So best to make stakes that require painful sacrifice, genuinely thinking outside the box, or overcoming limitations or long-running faults in order to succeed. That's where things are gripping and intense.
Having a room down the hall with guards that have a chance of hearing something seems like a thing. Only rolling of the party is doing well (if bad guy reinforcements) or doing badly (if good guy reinforcements) seems close enough to me to fudging I don't see a significant difference. Others mileage obviously varies.
I guess? I might just forget TBH. But diegetic references to this ("this is the second time reinforcements have arrived when your enemy was on the ropes...something is going on here, deeper than it appears") are a way to make these alterations story-contributing, actually justified even if technically after the fact, rather than fudging.
It feels immeasurably sad to me that some people approach every game they're in with friends expecting that someone is cheating and being hypersensitized to it.
Well, in fairness, most of my games have been with people who
weren't my friends before we started playing.
I don't personally think the rhetorical question is very useful here. Obviously not. To openly say such a thing would be pretty foolish. But I have absolutely seen people (don't think I've seen it in this thread) who are
intensely agitated by the merest hint of "player entitlement," but who (openly) think DMs are
slaving away for their ungrateful, petulant, flippant players, and thus inherently deserve unlimited trust and respect at all times no matter what techniques they employ. So, while they may not
explicitly believe DM entitlement is impossible, their explicit arguments do hinge upon such a thing being impossible.
How would the players know something in 5e that their passive perception checks failed to catch?
Because you
tell them. Using a system which doesn't allow secret checks (which is what Dungeon World does) forces you to not rely on stuff that could only be known via secret checks. I consider this a valuable lesson for the GM.
Isn't passive perception exactly designed to tell what they perceive about hidden things they aren't actively trying to spot?
In some senses, yes. In other senses, no. I am confident you don't consult passive perception every single time you need to describe a room to the party. You just describe it. Being forced to use a system where you
cannot rely on such passive and/or secret checks forces you to be evocative, specific, and thorough: you don't have the
luxury of leaving out details that can be picked up via passive perception.