There’s a great post over on Tales of the Grotesque and Dungeonesque about "Two Reasons Why Call of Cthulhu is One of the Great Horror RPGs." One of those reasons is the Sanity mechanic, which does an excellent job of simultaneously evoking an in-game effect on the characters and creating out-of-game tension with the players. I think the only other mechanic that has a similar effect is old school level drain, which made undead fully as terrifying to players as to their player characters. As the post points out,
Used liberally, Sanity loss in Call of Cthulhu is an unstoppable spiral into the abyss. Players should be incentivized to involve their character in the scenario for an important reason (stopping something awful from happening, keeping the people they love safe, etc.), but the act of involving their characters should also always put them in a position where losing precious Sanity is a preeminent threat.
But if Sanity is a great game mechanic, it is also “a poor representation of actual mental illness.” There’s just no getting around that fact. (Hit Points are probably an equally poor representation of physical trauma, too, but that’s a discussion for another time.)
But what if the biggest problem with the Sanity mechanic is just one of terminology. What if, instead of calling it Sanity, we called it … Humanity. Humanity is nice, abstract, and isn’t an actual mental health term. But more importantly, it perhaps better reflects the actual genre phenomenon. Fundamentally, Call of Cthulhu characters really aren’t so much threatened by loss of their rational minds—that’s just a symptom—as the loss their very humanity by contact with alien horror.
Alas, I rarely have the opportunity to play Call of Cthulhu but I do occasionally use the Sanity mechanic in Traveller (detailed in Traveller5 as well as in the Mongoose Traveller Companion) to model the effect of post-humanist technology. Personality copying, consciousness transfers, exposure to alien and AI tech, even anagathic drugs could potentially be balanced through use of the Sanity mechanic but again, Humanity is really what we are talking about here: the potential loss of a Traveller’s humanity through repreated exposure to posthumanist tech. Consider, for example, the Ghouls from the old Regency Sourcebook:
One of the most visible symbols of the disenfranchised nobility are the so-called “Ghouls,” young (by apparent age anyway), nihilistic, disenfranchised nobles who spend their dissipated lives and what remains of their noble fortunes by seeking excitement in personal and various near-death experiences (16).
The Ghouls basically suffer from loss of Humanity due to use of a new drug, Anagathic B, which also induces jumpspace intolerance into the users.
