2. 'Think and Grow Rich,' by Napolean Hill
This classic of the self-help genre was first published in 1937 – at the height of the Depression – and remains today one of the bestselling business books of all time. To write this book, Hill examined 40 millionaires in an attempt to discover the secrets of their success and then endeavored to impart their accrued knowledge to readers. At the core of the book are 13 principles that make up a philosophy of personal achievement which Hill believed could help anyone to succeed in any field – not just business. Hill himself worked for Andrew Carnegie and was acquainted with Henry Ford and Franklin Delano Roosevelt, among others.