Stephen R. Covey (1994). “Daily Reflections for Highly Effective People: Living THE SEVEN HABITS OF HIGHLY SUCCESSFUL PEOPLE Every Day”, p.108, Simon and Schuster
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.248, Simon and Schuster
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.250, Simon and Schuster