Glenn R. Schiraldi (2007). “10 Simple Solutions for Building Self-Esteem: How to End Self-Doubt, Gain Confidence, & Create a Positive Self-Image”, p.9, New Harbinger Publications
Clayton Christensen, Michael Raynor, Jeff Dyer, Hal Gregersen (2013). “Disruptive Innovation: The Christensen Collection (The Innovator's Dilemma, The Innovator's Solution, The Innovator's DNA, and Harvard Business Review article "How Will You Measure Your Life?") (4 Items)”, p.11, Harvard Business Press