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.568, Mango Media Inc.
Stephen R. Covey (1994). “Daily Reflections for Highly Effective People: Living THE SEVEN HABITS OF HIGHLY SUCCESSFUL PEOPLE Every Day”, p.159, Simon and Schuster
Stephen R. Covey (1994). “Daily Reflections for Highly Effective People: Living THE SEVEN HABITS OF HIGHLY SUCCESSFUL PEOPLE Every Day”, p.201, Simon and Schuster