John Danhakl, a managing partner at the private-equity firm Leonard Green & Partners, has helped launch seven funds over the past 30 years. Each of the funds has either already doubled its initial investment, or is on pace to do so, according to Danhakl. He also says they've seen an average gross return of 35%. As part of a panel discussion at the recent Milken Institute Global Conference, Danhakl shared the nine most important lessons he's learned from his three decades of experience. Visit Business Insider's homepage for more stories.