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).)
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).)