Brian Tracy (2008). “Eat That Frog!: 21 Great Ways to Stop Procrastinating and Get More Done in Less Time: Easyread Super Large 20pt Edition”, p.5, ReadHowYouWant.com
Stephen R. Covey (2015). “The Stephen R. Covey Interactive Reader - 4 Books in 1: The 7 Habits of Highly Effective People, First Things First, and the Best of the Most Renowned Leadership Teacher of our Time”, p.218, Mango Media Inc.