Billionaire David Rubenstein explains why he admires Warren Buffett – and lays out the traits shared by the world’s best investors Warren Buffett''s intellect, focus, and passion for investing are admirable, David Rubenstein said. The Carlyle Group cofounder interviewed several of the world''s elite investors for his upcoming book. The billionaire investor found them to be surprisingly humble, contrarian thinkers, and workaholics. David Rubenstein admires Warren Buffett''s intellect, focus, and love of investing for its own sake instead of the luxury lifestyle it can fund, Fox Business reported this week. "He has pretty good instincts and intuition," the billionaire investor and Carlyle Group cofounder said at the National Book Festival on Saturday, according to Fox. Rubenstein has spent the last year studying and interviewing top investors such as Ray Dalio, Seth Klarman, and Stanley Druckenmiller for his upcoming book, "How to Invest: Masters on the Craft." His comments speak to Buffett''s business acumen, how the Berkshire Hathaway CEO makes concentrated bets and rarely strays outside his "circle of competence," and Buffett''s joke that he "tap dances to work" because he enjoys his job so much.