The Tomb, the Original Short Story:

In relating the circumstances which have led to my confinement within this refuge for the demented, I am aware that my present position will create a natural doubt of the authenticity of my narrative. It is an unfortunate fact that the bulk of humanity is too limited in its mental vision to weigh with patience and intelligence those isolated phenomena, seen and felt only by a psychologically sensitive few, which lie outside its common experience. Men of broader intellect know that there is no sharp distinction betwixt the real and the unreal; that all things appear as they do only by virtue of the delicate individual physical and mental media through which we are made conscious of them; but the prosaic materialism of the majority condemns as madness the flashes of supersight which penetrate the common veil of obvious empricism.