Stephen R. Covey, A. Roger Merrill, Rebecca R. Merrill (1997). “First Things First Every Day: Daily Reflections- Because Where You're Headed Is More Important Than How Fast You Get There”, p.361, Simon and Schuster
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