For the past six weeks, I've been hard at work writing my “introduction to financial independence and early retirement” project for Audible and The Great Courses. It's been challenging — and fun — to rework my past material for a new audience in a new format. Naturally, I'm emphasizing two important points in this project: profit and purpose. I believe strongly that you need a clear personal mission statement in order to find success with money (and life). I also believe that the most important number on your path to financial freedom is your personal profit, the difference between your income and your spending.