General MotorsFalling markets? No problem.Amid all the of doomsday predictions and fearful hand-wringing about the stock market, the knowing chuckle of billionaire investor Warren Buffett once again puts panic into context. Of course he's buying stocks. Prices are falling, so why not? Like with his famous “hamburger quiz,” the best time to buy any asset is when it's cheaper, not when it's more expensive. As stocks fell last week, Buffett was buying. He was likely to buy anyway, he said. Lower prices just made it easier. “I like buying it as it goes down, and the more it goes down, the more I like to buy,” Buffett told CNBC. The typical Buffett quote that gets trotted out in turbulent markets applies: “Be fearful when others are greedy and greedy when others are fearful.” For retirement investors, though, there's another, more apt quote. “Only when the tide goes out do you discover who's been swimming naked.” Apt because the first quote relates more to how traders think. If you have a strong conviction on an investment and others seem to hate it, then buy without hesitation. If everyone loves a stock you own, watch out. By MITCH TUCHMAN