.While the book's title and much of the text concerns increased income, the author insists that the philosophy taught in the book can help people succeed in any line of work, to do and be anything they can imagine.First published during the Great Depression at the time of Hill's death in 1970, Think and Grow Rich had sold more than 20 million copies, and by 2015 over 100 million copies had been sold worldwide. It remains the biggest seller of Napoleon Hill's books. BusinessWeek magazine's Best-Seller List ranked it the sixth best-selling paperback business book 70 years after it was published. Think and Grow Rich is listed in John C. Maxwell's A Lifetime Must Read Books List. A good part of Hill's book is simply the gospel of 20th century American Capitalism: work hard, have a firm handshake, get ahead by doing quality work, treat your customers with respect, anybody can become rich and/or powerful if they overcome their personal weaknesses. Some may find the core 'secret' of this book elusive; Hill never gives us a succinct formula to acquiring wealth, although he hints that it exists. However, the title of the book is 'Think and Grow Rich,' not 'Get Rich Quick': Hill insists that we take a very detailed personal inventory, and grow spiritually, in order to draw wealth our way. This involves a developing a high level of self-discipline and obeying the Delphic injunction to 'Know Thyself'. He also incorporates a lot of good, practical business advice: find new opportunities created by technological innovations, make a written plan and keep to it, don't be afraid to fail repeatedly. The secret is here, it is just simply the sum of parts rather than an explicit roadmap.