Spoilers Ahead...
Numerous times in Bloodborne, there is mention of different people encountering 'the eldritch truth,' including the Byrgenwerth scholars, the Pthrmarians, and even an anonymously mentioned doctor and his sister. Some are glad to encounter it, and nearly all who encounter it have gone mad to some degree. But what could it be? It seems to be connected to the Kin, but I don't know for certain. Is it the simple knowledge of the Great Ones? Was it the finding/killing of Mother Kos at the Fishing Hamlet years ago, and had those fishermen been blessed by it? Or is it something more (or less)?
What is the eldritch truth?