Frictional have been open about the Lovecraft debt across the series, and the design turns one of his ideas into a rule: the protagonist cannot fight, and looking at the thing damages the mind. A sanity meter that drains in darkness and in the presence of the monster is The Call of Cthulhu's central claim made mechanical, that knowledge of what is out there is itself the injury. The fragmented documents the player reads are Lovecraft's found-manuscript structure too.