The Master Key System by Charles F. Haanel [1919]

Is there a secret behind the Secret? If so, this might be it. Haanel, a somewhat mysterious figure who was what we would today call a business development consultant, wrote this series of lessons shortly after World War I. This turbulent time was made even more miserable by a flu pandemic which killed millions. Many were searching for a royal road to prosperity, health and inner peace, and Haanel's book held out this promise.

For years, urban legends have swirled around this book: that it was banned by some religious groups, and central to the success of a certain well-known software tycoon. I was unable to confirm or disprove any of these rumors. However, the Master Key System has had a huge influence on successive New Thought writers, particularly those preaching 'Prosperity Consciousness.' Think and Grow Rich bears more than a passing resemblance to the Master Key System. The 'Law of Attraction' at the heart of Haanel's system has been acknowledged as one of the primary sources for The Secret.