xy

Fiction, The Call of Cthulhu (1926)
Context: It was from the artists and poets that the pertinent answers came, and I know that panic would have broken loose had they been able to compare notes. As it was, lacking their original letters, I half suspected the compiler of having asked leading questions, or of having edited the correspondence in corroboration of what he had latently resolved to see.

“One of those creatures wrote you once, ‘do not call up any that you can not put down’.”

H.P. Lovecraft book The Case of Charles Dexter Ward

often phrased as "Do not call up that which you cannot put down."
Fiction
Source: "The Case of Charles Dexter Ward", written 1927, first published in Weird Tales, July 1941

“The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents.”

H.P. Lovecraft (1890–1937) American author

Fiction, The Call of Cthulhu (1926)
Context: 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.

“I could not help feeling that they were evil things -- mountains of madness whose farther slopes looked out over some accursed ultimate abyss.”

H.P. Lovecraft (1890–1937) American author

Source: At the Mountains of Madness and Other Tales of Terror

“The basis of all true cosmic horror is violation of the order of nature, and the profoundest violations are always the least concrete and describable.”

H.P. Lovecraft (1890–1937) American author

Source: Selected Letters III: 1929-1931

“I like coffee exceedingly…”

H.P. Lovecraft (1890–1937) American author

“No new horror can be more terrible than the daily torture of the commonplace.”

H.P. Lovecraft book Ex Oblivione

"Ex Oblivione"
Fiction

“I am so beastly tired of mankind and the world that nothing can interest me unless it contains a couple of murders on each page or deals with the horrors unnameable and unaccountable that leer down from the external universes.”

H.P. Lovecraft (1890–1937) American author

“Bunch together a group of people deliberately chosen for strong religious feelings, and you have a practical guarantee of dark morbidities expressed in crime, perversion, and insanity.”

H.P. Lovecraft (1890–1937) American author

Letter to Robert E. Howard, (October 4, 1930), https://books.google.com/books?id=rVERL_j9UfcC&printsec=frontcover&dq=isbn:0809515679&hl=en&sa=X&ei=-beOVeGqHsi_ggT1vqKgCw&ved=0CB4Q6AEwAA#v=onepage&q=insanity&f=true <br class="br">Non-Fiction, Letters, to Robert E. Howard <br class="br">Context: It is the night-black Massachusetts legendry which packs the really macabre 'kick', Here is the material for a really profound study in group neuroticism; for certainly, no one can deny the existence of a profoundly morbid streak in the Puritan imagination.... The very pre-ponderance of passionately pious men in the colony was virtually an assurance of unnatural crime; insomuch as psychology now proves the religious instinct to be a form of transmuted eroticism precisely parallel to the transmutations in other directions which respectively produce such things as sadism, hallucination, melancholia, and other mental morbidities. Bunch together a group of people deliberately chosen for strong religious feelings, and you have a practical guarantee of dark morbidities expressed in crime, perversion, and insanity. This was aggravated, of course, by the Puritan policy of rigorously suppressing all the natural outlets of excuberant feeling--music, laughter, colour, pageantry, and so on. To observe Christmas Day was once a prison offence....

“Blue, green, grey, white, or black; smooth, ruffled, or mountainous; that ocean is not silent.”

H.P. Lovecraft (1890–1937) American author

“Through all this horror my cat stalked unperturbed. Once I saw him monstrously perched atop a mountain of bones, and wondered at the secrets that might lie behind his yellow eyes.”

H.P. Lovecraft book The Rats in the Walls

Source: The Rats in the Walls

“The appeal of the spectrally macabre is generally narrow because it demands from the reader a certain degree of imagination and a capacity for detachment from everyday life.”

H.P. Lovecraft (1890–1937) American author

“Creative minds are uneven, and the best of fabrics have their dull spots.”

H.P. Lovecraft (1890–1937) American author

“In short, the world abounds with simple delusions which we may call "happiness", if we be but able to entertain them.”

H.P. Lovecraft (1890–1937) American author

Letter to "The Keicomolo"—Kleiner, Cole, and Moe (October 1916), in Selected Letters I, 1911-1924 edited by August Derleth and Donald Wandrei, pp. 26-27
Non-Fiction, Letters
Context: Frankly, I cannot conceive how any thoughtful man can really be happy. There is really nothing in the universe to live for, and unless one can dismiss thought and speculation from his mid, he is liable to be engulfed by the very immensity of creation. It is vastly better that he should amuse himself with religion, or any other convenient palliative to reality which comes to hand. … There is much relief from the burden of life to be derived from many sources. To the man of high animal spirits, there is the mere pleasure of being alive; the Joi de vivre, as our Gallick friends term it. To the credulous there is religion and its paradisal dreams. To the moralist, there is a certain satisfaction in right conduct. To the scientist there is the joy in pursuing truth which nearly counteracts the depressing revelations of truth. To the person of cultivated taste, there are the fine arts. To the man of humour, there is the sardonic delight of spying out pretensions and incongruities of life. To the poet there is the ability and privilege to fashion a little Arcadia in his fancy, wherein he may withdraw from the sordid reality of mankind at large. In short, the world abounds with simple delusions which we may call "happiness", if we be but able to entertain them.