Wallace D. Wattles (2015). “The Science of Being Great: Personal Self-Help Book of Wallace D. Wattles (Unabridged): From one of The New Thought pioneers, author of The Science of Getting Rich, The Science of Being Well, How to Get What You Want, Hellfire Harrison, How to Promote Yourself and A New Christ”, p.39, e-artnow
Hugh Prather, Gerald Jampolsky (2000). “The Little Book of Letting Go: A Revolutionary 30-Day Program to Cleanse Your Mind, Lift Your Spirit and Replenish Your Soul”, p.10, Conari Press