From the Q&A: What is the Sanity ('SAN') mechanic in Call of Cthulhu?

[MOB]

From our Fan Use and Licensing Q&A:

Q: What is the Sanity ('SAN') mechanic in Call of Cthulhu?

A: Sanity (abbreviated as 'SAN') is the game mechanic in Call of Cthulhu that models the behavior of protagonists in Mythos fiction when confronted with incomprehensible physics and monstrous entities from beyond space and time. The cosmic horrors of the Cthulhu Mythos defy safe or easy comprehension. When faced with such terrors, the human mind attempts to rationalize them but may be corrupted by the experience. The acquisition of Cthulhu Mythos skill points in the game reflects an investigator developing a human-centric understanding of the Mythos, while the loss of SAN points balances this acquisition with the cost associated with this new, but terrible knowledge. In this sense, SAN is a corruption of human morals, behavior, and personality.

"Sanity" is the game’s register of the investigator’s mental resilience. It is not designed to model or make light of real-world mental health conditions, in the same way that hit points (and the loss of them) in most RPGs do not make light of real-world physical trauma and injury.

[DreadDomain]

It would also be useful to explain what it could mean to have low sanity or zero sanity. I've always thought that it represents the breakdown of the mind, or the loss of connection to human-accepted reality, or the corruption of the mind, all under the pressure of intense stress or exposure to the truth of the mythos. 

However, I don't think it necessarily leads to being completely dysfunctional, babbling and only good for the asylum. When Sanity, our human-constructed comprehension of what reality is, is fractured, it can drive you mad. But when the loss is counter-balanced with the understanding of the mythos, a connection with another reality, another paradigm is reconstructed. I believe this is why cultists can still function in society, hidding in plain sight. Lower level cultists or mythos dabblers will still act strange, having only started to pull the veil of the mythos but with a higher comprehension, say 50% or higher in Mythos, they have then a firm grip in the new paradigm, perceive the lies of the human-accepted world and can behave accordingly.

Edited January 28, 2022 by DreadDomain

[Aerinyes]

Zero SAN absolutely does not rule out being a high-functioning individual. Just look at all the NPCs with zero SAN, and what they are capable of accomplishing.

I would definitely question the motivations, morals, ethics, strategies, and tactics of such people, however, which may be why PCs with zero SAN are effectively removed from control of the player.