Robert Collier (2013). “The Secret of the Ages: The Secret Edition - Open Your Heart to the Real Power and Magic of Living Faith and Let the Heaven Be in You, Go Deep Inside Yourself and Back, Feel the Crazy and Divine Love and Live for Your Dreams”, p.14, Lulu Press, Inc
Robert Collier (2013). “The Secret of the Ages: The Secret Edition - Open Your Heart to the Real Power and Magic of Living Faith and Let the Heaven Be in You, Go Deep Inside Yourself and Back, Feel the Crazy and Divine Love and Live for Your Dreams”, p.25, Lulu Press, Inc
Robert Collier, Dr Robert C. Worstell (2014). “Robert Collier Copywriting Course - Masters of Marketing Secrets: Learn to Write Sales Letters That Pay”, p.140, Lulu.com
Robert Collier (2013). “The Secret of the Ages: The Secret Edition - Open Your Heart to the Real Power and Magic of Living Faith and Let the Heaven Be in You, Go Deep Inside Yourself and Back, Feel the Crazy and Divine Love and Live for Your Dreams”, p.13, Lulu Press, Inc
Robert Collier (2013). “The Secret of the Ages: The Secret Edition - Open Your Heart to the Real Power and Magic of Living Faith and Let the Heaven Be in You, Go Deep Inside Yourself and Back, Feel the Crazy and Divine Love and Live for Your Dreams”, p.104, Lulu Press, Inc