The Call of Cthulhu by H. P. Lovecraft
Published February 1928 in Weird Tales, Vol. 11, No. 2, p. 159-78, 287.
 

The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents.
We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we
should voyage far. The sciences, each straining in its own direction, have hitherto harmed us little; but some
day the piecing together of dissociated knowledge will open up such terrifying vistas of reality, and of our
frightful position therein, that we shall either go mad from the revelation or flee from the light into the peace
and safety of a new dark age.

Theosophists have guessed at the awesome grandeur of the cosmic cycle wherein our world and human race
form transient incidents. They have hinted at strange survivals in terms which would freeze the blood if not
masked by a bland optimism. But it is not from them that there came the single glimpse of forbidden eons
which chills me when I think of it and maddens me when I dream of it.