Inspired by:

https://licheslibram.blogspot.com/2023/09/socially-appropriate-noesis-how-i.html?m=1 (Please read it, as I assume that you did. This text is an attempt at realization of the given idea)

Sanity Score

Is the number of core beliefs that you hold. You may not go over 10, with most people starting at 7. Write down each of your character's core beliefs with a pencil - each time one of their beliefs is attacked by their surroundings (regardless if it's a psychoanalyst deconstructing their personality, or a person believing in objective beauty seeing something they consider ugly praised) roll a sanity loss save (as dictated by the used system). If you succeed, you manage to rationalize the thing that would damage your belief away. If not, remove the belief and lose 1 SAN point.

After a month spent acting out a given belief system you may decide to adopt it in earnest - if so, then add a new belief and a SAN point.

High and low SAN

High SAN (Bigger than 7) usually shows as a person who has many sincerely held beliefs. They may have trouble integrating so many things into their worldview causing cognitive dissonance, or they may do so effortlessly with a coherent worldview. Either way, they are confident that they know what they're doing.

Low SAN (3 or less) is not so pretty. A person with low SAN has nothing to grasp onto. They may be terrified of their surroundings, or blissfully unaware, but in either case they have trouble functioning in any form of society. They may hold on to the remains of their prior beliefs out of habit, but it will take a long time for them to rebuild their zeal.

Example Values and example things that may damage them

There is objective good and evil: contact with creatures that have alien morality to yours.

Truth exists and brings goodness into the world: witnessing damage created by informational hazards. Being forced to lie to save a life.

There is an immortal soul: receiving or witnessing the effects of brain damage or the similar.

Through hard work, one may achieve their goals: Having contact with the idle rich, having one's life work destroyed.

Killing is wrong: being forced to kill in self defense.

We are important: having contact with the vastness of space.

It will fundamentally work out in the end: witnessing great atrocities that spent a long time uncontested.

There is a good God: having contact with worshippers or other emanations of evil or indifferent gods.

I can trust my senses: having one's senses muddled by illusions, finding out that one's life is a lie.