The biggest hurdle is rejection. Any business you start, be ready for it. The difference between successful people and unsuccessful people is the successful people do all the things the unsuccessful people don't want to do. When 10 doors are slammed in your face, go to door number 11 enthusiastically, with a smile on your face.
At least once a year, I meet with a group called the Giving Pledge. It's a group of billionaires - including me, Warren Buffett, Bill Gates, and Ted Turner - who have pledged to give away most of their money to charity. We meet for three days to talk about what we're doing to help make the planet a better place to live.