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Warren Buffett (left) and Charlie Munger.
  • Warren Buffett's Japan trade was a rare chance to win big with minimal risk, Charlie Munger said.
  • Berkshire Hathaway borrowed money at 0.5% in Japan and invested in stocks paying a 5% yield there.
  • "It was like having God just opening a chest and just pouring money into it," Munger said.

Warren Buffett's surprise bet on Japan during the pandemic was a once-in-a-lifetime chance to make a boatload of money with virtually zero risk attached, Charlie Munger says.