Well, yes, the fact that one D&D campaign is nothing like another even if both groups follow the rules closely is a very strong evidence.
Is Reinfield a main character in Dracula or just another freak who is there just to be off-putting? Eating bugs and being weird is what Reinfeld was born to do. He's just doing his job. The same doesn't apply to a damn protagonist.
I can't conceive any way to make a brave fighter eating dirt because he've seen a tentacled mess (and then being okay 1d10 minutes after) seem believable.
Mechanical teeth refers to teeth on a gear, not to teeth in a dragon's maw.
Wait.
Do I really need to explain that removing a player from a game for a considerable amount of time isn't a good idea in any RPG?
It gives gimmicks, not flaws. That, again, don't encourage using them to get your character in trouble.
That's not how game design works. The best, most effective move available to a player should always align with the tone of the story. With madness rules the best, most effective move is to say "no way I'm doing this" and "screw this naughty word, let's get outta here".
They don't reward the players for placing their characters into dire situations and driving them insane. On the contrary, the rules punish them for doing their job properly.
Dude. That's what this whole thread is about.
If the rules don't work for me and work for you, even if we both followed them, then... The rules don't produce reliable results and don't funnel the participants towards genre-appropriate experience. In short, they don't work.
Again, madness and sanity optional rules didn't make your campaign horror. You did.
Right, so for all its other flaws, the Call of Cthulhu game illustrates the above points.
First, SAN loss is not something you can avoid. While I think it is unwise for the Keeper to constantly 'garden' SAN checks, you surely cannot get far without exposing yourself to something nasty and taking SOME SAN loss. It is thus integral to the game.
Furthermore each point of Mythos skill you acquire costs you one permanent SAN loss. This faces each PC (certainly some PCs) with a devil's bargain, increase your skill rating in this vital area and break your mind, or you can try to remain largely ignorant and avoid SOME damage to your brain! The Keeper will surely inflict this dilemma on the PCs on a regular basis, "Oh, look a copy of the Book of Eibon lying open on the bad guy's desk. Do you want to study it?"
Spell casting costs SAN directly. EVERY SINGLE time you access this resource, of potentially almost limitless utility, you burn SAN! While CoC isn't a high magic game by any means, spells are darned handy and a constant temptation. This is ANOTHER devil's bargain!
There is no question about how to use the SAN mechanic, or really even WHEN to use it. The rules are very clear, they contain a whole list of situations and what sort of SAN loss they entail. Every single creature, spell, book of lore, etc. spells out exactly what the SAN consequences of interacting with it are. Furthermore these are scaled, so seeing a dead guy with his eyes chewed out by rats is worth something like 0/1d6, and seeing Cthulhu himself rise from the depths of the ocean is a straight up 1d100 SAN loss experience (most PCs are basically insta-ganked by this).
The effects of SAN loss are also very clearly spelled out. 5 points worth causes temporary insanity, and it is explained what that means in an RP sense and how the Keeper should handle it, how and when the PC recovers, etc. (this amount still allows you to function with some potential problems). Greater losses can cause permanent, but curable, insanity, as long as your total SAN remains above zero. Again, there are rules for how this works and you can at least still participate in the adventure on some level with the PC, but it will have to be cured later. Finally zero SAN is described as basically a PC Kill, though your character might still work as an NPC in some capacity (IE be consulted while ranting in a straight jacket in Arkham Asylum). There are also rules for GAINING SAN. You can gain it for defeating monsters (but never as much as you probably lost) and cultists, or through paying in time and money to have therapy, though that can only provide limited help.
In other words, this is a highly integrated subsystem which presents players with hard choices and models the characters descent into madness as a process. It also doesn't include things like random tables of symptoms and such. In fact I think in 7th Gen they mostly avoid much in the way of diagnostic terminology. At most there are suggestions like "the Keeper might declare that the character has acquired a paranoia or phobia" or something like that. Mechanical consequences are pretty loose, actually, but include the Keeper imposing hallucinations or compulsions. Failing a SAN check also temporarily incapacitates the character, even if it doesn't lead to any other effect (IE they turn away, run, cower in fear, vomit uncontrollably, or something like that instead of acting for a brief moment).
Obviously, with enough work, you could integrate a framework like that onto a game like 5e, but nothing like that has been done. This is POSSIBLE, but requires more work and some genre bending changes to the system.
