Canada Month, June 1963. A later satirical version of this saying added to the end "Luckily, this is not difficult" (Paul Dickson, The Official Rules [1978]). See Eleanor Roosevelt 2
"Q&A with Arianna Huffington, co-founder of Huffington Post, on Donald Trump, sleep and the media". Interview with Laura Newberry, www.masslive.com. April 29, 2016.
"Incredible Quotations: 230 Thought-Provoking Quotes with Prompts to Spark Students' Writing, Thinking, and Discussion". Book by Jacqueline Sweeney, 1997.