And sure enough, the greed got seriously out of hand and then imploded, in fact twice, once with the bursting of the stock market bubble of 2000, and then even more seriously with the real estate and sub-prime mortgage bubble and resulting financial meltdown of 2008-2009.

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In the case of the U.S. economy now, the double-whammy of wealth shocks from the real-estate bubble and the stock-market crash has made consumers understandably cautious.

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If the real estate bubble bursts, it may produce a rerun of 2008, when the Shanghai stock market plunged about 60%.

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Fearing a bubble, government officials have taken a myriad of steps to reign in the breakneck growth of the real estate market.

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