Friendship is evanescent in every man's experience, and remembered like heat lightning in past summers.
(Henry David Thoreau (1817-1862), U.S. philosopher, author, naturalist. A Week on the Concord and Merrimack Rivers (1849), in The Writings of Henry David Thoreau, vol. 1, p. 277, Houghton Mifflin (1906).)
Do not speak like a death's-head, do not bid me remember mine end.
(William Shakespeare (1564-1616), British dramatist, poet. Falstaff, in Henry IV, Part 2, act 2, sc. 4, l. 234-5.
"Death's head" means skull, used as a memento mori or reminder that death awaits everyone.)
Those who cannot remember the past are condemned to repeat it.
(George Santayana (1863-1952), U.S. philosopher, poet. Life of Reason, "Reason in Common Sense," ch. 12 (1905-6).
William L. Shirer made these words the epigraph for his Rise and Fall of the Third Reich (1959).)