“Whence come those mysterious influences which change our happiness into discouragement, and our self-confidence into diffidence? One might almost say that the air, the invisible air, is full of unknowable Forces, whose mysterious presence we have to endure. I wake up in the best of spirits, with an inclination to sing in my heart. Why? I go down by the side of the water, and suddenly, after walking a short distance, I return home wretched, as If some misfortune were awaiting me there. Why? Is it a cold shiver which, passing over my skin, has upset my nerves and given me a fit of low spirits? Is it the form of the clouds, or the tints of the sky, or the colors of the surrounding objects which are so changeable, which have troubled my thoughts as they passed before my eyes? Who can tell?”
— “The Horla” by Guy de Maupassant
Another classic horror story I’m linking to in honor of Satan, I mean, er, Halloween.