Bryan Sheffield

Sheffield is no stranger to volatility. He founded his Austin-based oil and gas company in 2008, and expanded it during the ensuing economic down years, leasing thousands of acres in the Midland Basin. It's been a wild ride since, with a successful IPO in 2014 that made Sheffield a billionaire, followed by years of sinking oil prices. Today, the price of a barrel is floundering around the $50 mark. But Parsley Energy is ramping up production. The quality that has most helped him succeed? "Optimism – the ability to view challenges as opportunities – has buoyed Parsley Energy during the inevitable tough times," he told Fortune. The quality that's sometimes detrimental? Also optimism, he says, i.e. "the stubborn belief that things will work out for the best."