In "The Man Who Found Out (A Nightmare)" by Algernon Blackwood, readers are taken on a chilling and unsettling journey into the world of the occult and the supernatural. The story follows a man who becomes obsessed with unlocking the mysteries of the universe, only to discover the horrifying truth that some secrets are better left undiscovered.

Blackwood's writing is atmospheric and evocative, creating a sense of dread and unease that lingers long after the story is finished. The protagonist's descent into madness is depicted in a hauntingly realistic way, leaving readers questioning the nature of reality and the limits of human understanding.

The pacing of the story is excellent, building tension gradually until the final, shocking revelation. Blackwood's ability to blend psychological horror with supernatural elements makes for a truly unforgettable read.

Overall, "The Man Who Found Out (A Nightmare)" is a masterful piece of horror fiction that will leave readers questioning their own beliefs and fears. It is a must-read for fans of the genre and anyone who enjoys a good scare.

Book Description:
A researcher goes on an expedition to find "The Tablets of the Gods" which have plagued his dreams since his boyhood. He finds them, and the horrible truth of humanity's true purpose in the universe. This story, The Man Who Found Out" is an example to me of pure cosmic horror in that the horror comes totally from knowledge which is (in-story) so terrible that it forever blights the minds of anyone who discovers it. Two highly intelligent and well informed men, Professor Ebor and then Dr. Laidlaw, learn the contents of the Tablets of the Gods, and even though this information is short enough to be on two ordinary-sized tablets, it is enough to induce absolute belief in its veracity and utterly destroy hope in the reader. Yeah, that is pretty scary. There are no monsters in the tale, nothing but Forbidden Knowledge -- which, apparently, is Forbidden with good reason. (Wikipedia and the reader )