8 Unbreakable Rules For Success I speak with Sean Castrina about his book 8 Unbreakable Rules For Business Start-Up Success. Sean shares, in brief, the 8 principles that he has found to be the key to business success, not only in his world but in all successful business start-ups. If you cannot afford to fail, this is the one book you want to read. Guest Bio. Sean Castrina is a serial entrepreneur, having started more than 20 companies over the last 20 years, and still seeks to launch a new venture annually. He is an investor, teacher and highly-sought-after speaker who communicates with humor and a bluntness that engages and captures his audience. He is the author of 8 Unbreakable Rules for Business Startup Success, The Greatest Entrepreneur in the World, and World's Greatest Business Plan.