I don't follow.
Falling can kill you. A pillow mitigates the consequences of falling. A big enough fall will kill you. A big enough pillow will save your life if you fall.
But a pillow can't "actively remove things that can kill you" (by your standards, as I understand them, it offers damage reduction, but not healing).
Whereas what I had in mind is that, when my toddler falls over, she could die (from hitting her head on the footpath). But happily she hasn't yet! - and she is up and going again once I "kiss her better". That is to say, to mitigate the consequences of this fall I don't have to be able to do things that would stop someone dying (you can't kiss a mortal wound better).
When Aragorn dreams of Arwen (in the Peter Jackson version) and revives, he is not the beneficiary of a power that can prevent death. The point is that, while he
might have been dying, he is not. And that is how warlord healing works in 4e (and second wind also, and in my view also all the "word" abilities).
This is part of what I sometimes call Schrodinger's Hit Points. Shortly, it's a problem when you decide after the fact that the attack was not potentially fatal.
I don't think it's a problem - though of course it's a significant feature of the ruleset.
AD&D had it too, with poison saves for example - you can't narrate the attack in full detail (did the stinger break the skin?) until the poison save is made. The Forge calls this "fortune in the middle", and characterises it as deferring the establishment of what is happening in the fiction until some furthter mechanical procedures are undertaken.
There's no doubt that the deferral in 4e can be longer (both in terms of ingame time, and mechanical procedures to be undertaken at the table) than in AD&D. But the principle is the same (which is why I've taken to posting "Schroedinger's Wounds!" every time someone who is critical of 4e posts in favour of AD&D-style saving throws - 3E, of course, changed saving throws to be much more like a skill mechanic without this sort of metagame dimension).
If D&D HP damage can kill you, you have to assume that all HP damage is done with the potential to kill, or you enter a position where you don't know what the HP damage represents until someone tries to heal it, at which point you invent some justification for why that healing works.
You don't
have to make that assumption - for example, if the kobold hits and the PC stays up, you don't have to assume that the blow had the potential to kill at all. And if, as is often the case, the hit is not narrated in much detail, it won't per se harm the game to spell it out in more detail later if that becomes necessary ("You notice blood oozing out from under your armour - maybe that kobold hit you harder than you thought!").
If the thing cannot kill you, it shouldn't be doing HP damage, because HP damage, mechanically, can kill you.
Obviously. But if it
doesn't kill you, then there's no need to narrate it as even potentially fatal if you don't want to.
If the thing can kill you, then effects that restore HP need to undo things that can kill you.
And I reiterate that this is a non-sequitur. Because if it
hasn't killed you, then narrating its mitigation or overcoming (which is what restoring hp would represent) need only establish something in the fiction sufficient for such mitigation or overcoming, which need not be something capable of undoing the threat of fatality. (And this is a good thing for recovering-hp-by-resting rules, because as a general rule
rest is not capable of undoing things that can kill you.)
That gets things entirely backwards from how the rest of the game is played, wherein the DM-player call-and-response is based on each one establishing some information about the game world.
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In D&D, which relies on a call-and-response core dynamic, it's important to know how to call and respond, and that relies on a shared knowledge of the current state of the game world.
I assume you don't treat the gameworld as a stop-motion one, even though this is how turn-based initiative presents it (especially in the playtest, with fewer out-of-turn actions than 4e or even 3E). So presumably you are deferring establishment of what actually happened in the fiction until every creatures has taken its turn - or something.
In fact, not even as simulationist a game as Runequest or Rolemaster satisfies your description of the establishment of the details of the shared fiction, because you don't know where a combatant aimed until after a hit is achieved and hit location is determined (in RM's case, via the roll on the critical chart plus the shield breakage roll).
Again, I'm not saying that 4e is not different. It is. But the difference is not one of radical kind. And therefore, saying that things
can't be that way, or
must be some other way, if the establishment of the shared fiction is going to proceed properly, is not true. (And that's putting to one side the many other RPGs besides 4e that have robust fortune-in-the-middle mechanics and are not known for being weak on story, like HeroWars/Quest, Maelstrom Storytelling, etc.)
There's problems for a LOT of people with an effect that cannot be defined until it is removed.
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Some groups have zero problem with this, and are more comfortable with a more gamist scenario where the game effect is justified by whatever fiction works, but that's not something that is necessary for a good D&D game, so the problems it DOES create seem far too vast to require that everyone play the game that way.
This has nothing to do with whether or not designs can or can't work, and can or can't achieve GM-player-GM "call and response" play. It is just reiterating what is notorious, that a lot of people don't like 4e's fortune-in-the-middle mechanics.
That's a legitimate point, but I think it's a mistake to frame it in terms of what the mechanics
must be if a certain sort of traditional RPG procedure is to work, given that there are many games that use the same procedure but lack your mechanical desiderata. HeroWars/Quest, Maelstrom Storytelling, Tunnels & Trolls and 4e all work on call-and-response, the same as AD&D and 3E. All have fortune-in-the-middle mechanics. And so do the latter two (saving throws and turn-by-turn initiative, respectively; and also hp, on the Gygaxian interpretation of them).
It is fairly easy to add back in once it's taken out.
I don't think this is necessarily true. My sense is that designing a game with good fortune in the middle mechanics is hard.