Thousands of personal finance books on shelves today promise to teach you to spend less, save more, invest better, retire earlier, get out of debt faster, and solve just about every financial conundrum in between.

But perhaps none said it better than a book Published in 1937.

Napoleon Hill, a Great Depression-era author and former advisor to President Franklin D. Roosevelt, interviewed "more than five hundred of the most successful men this country has ever known" to figure out the key to their good fortune. He wrapped all of his insights in a 200-page package and published "Think and Grow Rich," which went on to become one of the best-selling books of all time.

Don't expect to find any stock-picking or gambling advice in it. Despite Hill interviewing some of the most iconic businessmen of his day, none of his findings involved any particularly hard-to-attain skills. His entire premise is helping people overcome the psychological barriers that keep them from wealth.