William James: Act as if what you do makes a difference. It does.

Source

From the book Correspondence with Helen Keller, Correspondence with Helen Keller, 1908, in The Correspondence of William James: April 1908–August 1910, Vol. 12, Charlottesville: University of Virginia Press, 2004, page 135, as cited in: Academics in Action!: A Model for Community-engaged Research, Teaching, and Service (New York: Fordham University Press, 2016, page 71)