Quote Originally Posted by tuggyne View Post
Not entirely implausible. Now take elementals, which don't have frightful presence, but do have larger varieties that are fundamentally similar and yet harder to identify. How does that make sense?
Elementals probably should have frightful presence, or a similar ability. They're aspects of primordial chaos, things which are alive that are made of stuff that shouldn't be alive. The more elder and powerful they are, the more nearly they resemble the hoary and eldritch lords of their planes - indeed, if you know just a little about them, they're even more terrifying, because they're literally all small pieces of those ultra-elemental horrors. The only name I remember is Cryonax and there aren't always cold elementals, but if we assume there are, each and every cold elemental is really just a tiny piece of Cryonax, serving as his eyes and ears throughout the world he intends to conquer. So yeah, they ought to be frightening, and more so the more uber they are.

your first fight against dozens of dretches is undoubtedly terrifying in the extreme, but studying a single one may give you the key to all of them. And according to the rules a single dretch is dead easy to study: DC 12. "Hit 'em with Sound Burst!"
This is part of why there's a cap on CR scaling. If you are able to think of an easy way to kill them en masse, they aren't that scary. It's when that knowledge check fails that the fear sets in, and if you've invested lots of ranks in study, then you can't fail; you're a veteran demonologist and you know that dretches are pathetic, so there's no chance of you being frightened by the idea of them, even though there's some chance of you being killed if they get the drop on you. (What makes less sense is that a character with a +11 total Intelligence bonus can pick up a single rank and now he can never fail the check, despite having never had the option to try it previously; apparently if you're smart enough, knowledge just falls out of the air into your brain with virtually no effort the moment you deign to acknowledge the topic's existence by familiarizing yourself with it to a trivial extent.)

Then, too, it doesn't work if you're in no immediate danger
A cat has virtually no possibility of killing a human being (since we're not Level 1 commoners), and yet ailurophobia is fairly common. Other people are afraid of trees or even flowers, to say nothing of ophidiophobians reacting to a garter snake. Fear of a thing has very little to do with how much actual danger it poses.

When you see a creature that you've never seen before, the GM rolls to determine whether you're able to comprehend what you're looking at, and if the roll fails, one of the reasons that failure might have occurred is that your character's first reaction was blind, unlreasoning terror of the thing that isn't actually a threat to him. Maybe phobias are more common among the residents of D&D world; it's not like they don't have reason to live in a state of constant near-panic given how absurdly dangerous their reality is. (Indeed, perhaps that's why their society can't evolve beyond the medieval age; they keep being plunged back into the dark ages by witch-panics and plagues and such, and reason can never get a foodhold because the population as a whole is just too anxiety-riddled to be sensible on any unilateral basis.)

Finally, it would justify a fixed penalty on the knowledge check, quite possibly, but one that increases linearly?
Sure, why not?

Eh, fair enough; that one was a throwaway example of strict RAW that no one would likely follow anyway. (I believe Martial Lore is designed to act like Spellcraft for martial adepts, but I don't know of a Knowledge subskill for the purpose.)
I am now annoyed that they didn't name it Swordcraft or Warcraft, given that "Lore" is a word specifically associated with Knowledge checks.