François duc de La Rochefoucauld, Stanisław I Leszczyński (King of Poland) (1851). “Moral Reflections, Sentences and Maxims of Francis, Duc de la Rochefoucauld”, p.184
Robert H. Schuller (1993). “Robert H Schuller: The Inspirational Writings : Tough Times Never Last, But Tough People Do/Tough Minded Faith for Tender Hearted People”, Bbs Publishing Corporation