There's an idea that I see from time to time in setting design which I don't entirely get the appeal of, and that is the idea of the lethal setting. That is, there is some element of the setting which will kill or incapacitate characters unless they always do something arbitrarily dictated by the setting.
I'm not talking about merely dangerous settings, like the classic Dark Sun. I completely understand the appeal of that (dangerous environments are an escalation on existing tensions). Similarly, I don't mean frequent threats, like radiation in Gamma World. Those have their place, and it's obvious to me.
Rather, I'm thinking about ambient, ever-present dooms, like in the Red Steel setting, or some of the later (or maybe middle) Thoma Covenant books. The details don't matter a lot, as the underlying idea is the same. Something inescapable (like sunset or the air) will DO SOMETHING HORRIBLE to you unless you [MACGUFFIN].
The exact details of the macguffin don't really matter. It might be behavioral (like, you must stay out of the light, or must stand on rocks when the sun rises) or a resource (you must carry a piece of magic rock with you), but whatever the deal, if you break the taboo, the price is basically death. And, importantly, the macguffin is the only option - there is no way for a character to be clever or tough enough to get around this threat.
I can sort of faintly see why a setting designer might structure things this way. It provides a constant threat, if a bad one and it nominally introduces another thing to track and threaten (like fuel in a spaceship game), so you can introduce race the clock elements into play by occasionally taking away the macguffin and forcing players to run for it.
That's all well and good, but what I'm missing is the fun.
I don't ask this in a snarky way - this idea is not a rare one by any stretch, so there's something that that clearly resonates with some people, and I'm curious to know what it is. Any thoughts?
1 - It's a bad threat the same way the threat of an instakill is bad. Threatening player fun is a poor way to enforce fiction. Plus, any constant threat gets dull with repetition, and such threats are predicated on their predictability.