“Life is one long struggle in the dark.”
Book II, line 54 (tr. Rouse)
De Rerum Natura (On the Nature of Things)
Original
Omnis cum in tenebris praesertim vita laboret.
Help us to complete the source, original and additional information
Lucretius 45
Roman poet and philosopher -94–-55 BCRelated quotes

Source: Memory, Sorrow, and Thorn, Stone of Farewell (1990), Chapter 9, “Cold and Curses” (p. 211).

“Long, long may it be, ere he comes again! His hour is one of darkness, and adversity, and peril.”
"The Gray Champion" (1835) from Twice Told Tales (1837, 1851)
Context: Long, long may it be, ere he comes again! His hour is one of darkness, and adversity, and peril. But should domestic tyranny oppress us, or the invader's step pollute our soil, still may the Gray Champion come, for he is the type of New England's hereditary spirit; and his shadowy march, on the eve of danger, must ever be the pledge, that New England's sons will vindicate their ancestry.

“All is mystery; but he is a slave who will not struggle to penetrate the dark veil.”
Part 5, Chapter 18.
Books, Coningsby (1844), Contarini Fleming (1832)

"The Art of Living", interview with journalist Gordon Young first published in 1960
Source: Reprinted in C. G. Jung Speaking, ed. McGuire and Hull, pp. 451-452. link to Internet Archive https://archive.org/stream/MemoriesDreamsReflectionsCarlJung/carlgustavjung-interviewsandencounters-110821120821-phpapp02#page/n237/mode/2up

"The Two Streams", Ch. VI.
The Professor at the Breakfast Table (1859)

Source: Twenty Years at Hull-House (1910), Ch. 6

“One's life has value so long as one attributes value to the life of others.”