As A Man Thinketh is partly responsible for the creation of the entire personal development industry. Most contemporary PD authors and teachers credit this little book for providing foundation to their principles. It is a set of philosophical musings on the power of our thoughts. Earl Nightingale, widely regarded as the father of modern day personal development, in his best-selling recording, called the ideas in this book, "The Strangest Secret". The secret, he said, is "we become what we think about".