Sanity (SAN) is the core horror mechanic of Call of Cthulhu, designed by Sandy Petersen. An Investigator’s score drops whenever they encounter Mythos beings or forbidden tomes, and losing enough triggers temporary or longer-term madness.
Because the mind, not the body, is the resource at stake, the danger is comprehension itself. The notion of breaking as the price for learning what should not be known shares a register with our world’s dread.