It seems so long ago. But in 2009, many of the wealthy were stunned to find themselves in a cash crunch. Despite all the talk of cash cushions and risk management, many of the wealthy suddenly realized that they had overborrowed, overspent and overconcentrated on a single asset or industry.
We had suddenly entered the new age of the High-Beta Rich, where the wealth was volatile and far more cash was needed to absorb the shocks of financial markets.
Four years later, the lesson still holds.
A study from Spectrem Group asked wealthy and affluent investors "what do you wish you had done differently in the crisis."
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For the top earners—those making $750,000 or more—the No. 1 answer was "saved more." Ranked second was "done more research about finances on my own" and then "not taken on as much debt."
Their regrets have turned into real action—with possible impacts on the broader economy. Since the financial crisis, the wealthy have become the nation's top cash hoarders, filling up deposit accounts and money markets at a rapid clip.
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According to research from American Express Publishing and Harrison Group, the savings rate of the wealthiest 1 percent soared to 37 percent in the second quarter. That's up from 34 percent in the second quarter of 2012—and more than three times their savings rate in 2007.
A separate study from Bank of America recently found that 56 percent of millionaires have a "substantial" amount of cash. Only 16 percent of them plan to invest that cash in the next couple of months. And only 40 percent plan to invest it over the next two years.
Some say that cash is money that could be invested in companies, spent on consumer goods or put into job-creating enterprises. Still, stock markets and other financial assets are near all-time highs even with all that cash on the sidelines. And the spending by the wealthy remains fairly strong by most measures.
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Perhaps the wealthy are wise to keep more money on hand in case those record-breaking markets start to falter.
—By CNBC's Robert Frank. Follow him on Twitter @robtfrank.