Personal Development

You came across a personal development book called Think and Grow Rich? It is by Napoleon Hill.

He says in the preface of the Think and Grow Rich book, "IN EVERY chapter of this book, mention has been made of the money-making secret which has made fortunes for more than five hundred exceedingly wealthy men whom I have carefully analyzed over a long period of years. The secret was brought to my attention by Andrew Carnegie, more than a quarter of a century ago. The canny, lovable old Scotsman carelessly tossed it into my mind, when I was but a boy. Then he sat back in his chair, with a merry twinkle in his eyes, and watched carefully to see if I had brains enough to understand the full significance of what he had said to me."

What does he mean by "The Secret"?

Does "The Secret" have anything to do with "Personal Development"