John Bunyan (1811). “Choice Works: Containing Grace Abounding to the Chief of Sinners: Heart's Ease in Heart Trouble: The World to Come, Or Visions of Heaven and Hell: The Barren Fig-tree: and The River of Water of Life”, p.75
Ronald A. Heifetz, Marty Linsky, Alexander Grashow (2014). “Adaptive Leadership: The Heifetz Collection (3 Items)”, p.204, Harvard Business Review Press