“Attributed in Ray Josephs, "Robert Frost's Secret", in William Nichols (ed.) Words to Live By (Simon and Schuster, 1959), pp. 172-73. Also in Robert I. Fitzhenry (ed.) The Harper Book of Quotations (1993), p. 261, and in Richard Evans' Quote Book (Publishers Press, 1973), p. 109”

Source: Wikiquote