“Then it is that the height of unhappiness is reached, when men are not only attracted, but even pleased, by shameful things, and when there is no longer any room for a cure, now that those things which once were vices have become habits.”

The Dreamstone, Book One : The Gruagach, Ch. 1 : Of Fish and Fire
Arafel's Saga (1983)
Context: Things there are in the world which have never loved Men, which have been in the world far longer than humankind, so that once when Men were newer on the earth and the woods were greater, there had been places a Man might walk where he might feel the age of the world on his shoulders. Forests grew in which the stillness was so great he could hear stirrings of a life no part of his own. There were brooks from which the magic had not gone, mountains which sang with voices, and sometimes a wind touched the back of his neck and lifted the hairs with the shiver of a presence at which a Man must never turn and stare.
But the noise of Men grew more and more insistent. Their trespasses became more bold. Death had come with them, and the knowledge of good and evil, and this was a power they had, both to be virtuous and to be blind.

Source: Lock and Key

Source: Between Caesar and Jesus (1899), p. 16

Guardian Angel, p. 220
2000s and posthumous publications, The Collected Stories of Arthur C. Clarke (2001)
Source: Childhood's End

A New Slant on Life (1998).

55 Phocion
Apophthegms of Kings and Great Commanders

Quoted in Survey of Contemporary Literature (1977) by Frank Northen Magill, p. 4263

The Autocrat of the Breakfast Table (1858)