In an interview with CBS’ Sunday Morning, Warren Buffett says he’s not worried about the U.S. debt. A rising debt/GDP ratio isn’t good, he says, and the country does need to stabilize its debt/GDP ratio. But the overall debt itself “is not a problem,” he says, noting that the country’s debt/GDP ratio was higher coming out of World War II than it is today. Fortune writer Carol Loomis, a friend who has written often about Buffett through the years, is also interviewed. She says that Buffett’s greatest strength is his rationality — a trait most investors lack. Buffett also says that he thinks the average person should “buy all of America through an index fund”, putting money in bit by bit over time, rather than pick and choose individual stocks.