↑ Hubbard, Elbert (1922). Selected Writings of Elbert Hubbard. V. Wm. H. Wise & Co./The Roycrofters. p. 237. Archived from the original on September 8, 2012.
↑ Hinckle, Warren. If You Have a Lemon, Make Lemonade. W. W. Norton & Company. ISBN 0393306364.
