My friend “Roy” is a talented businessman and — in most respects — a natural-born entrepreneur. He’s made several fortunes in his life, but he’s lost them too. As I write this, he is starting over again — for the fourth time. “My life has been a roller coaster,” he said to me over a beer the other night. “And I don’t know why.”

I know why. When it comes to building wealth, Roy is missing one key characteristic. That characteristic?