It would be nice if there were a surefire and legitimate way to get rich quick. But there isn't.

According to a new study from Bank of America's US Trust, 77% of the firm's clients rose from middle class and poorer backgrounds to become high net worth (HNW) individuals by building their wealth slowly over time.

As for investing, do HNW individuals — those with at least $3 million in investable assets — have access to some secret trading strategy exclusive to rich people?

No. For the most part they employ a "basic, long-term approach to investing."

"Eighty-six percent of HNW investors made their biggest investment gains through long-term buy and hold strategies, traditional stocks and bonds (89%) and a series of small wins (83%) versus taking big investment risks. Their use of more sophisticated investments grows as their wealth increases."

"Buy and hold" is exactly what it sounds like. You buy what you think is a good stock, and then you hold on to it with the expectation that it may take a long time for the price to end higher.

Unfortunately, this is easier said than done, largely because of poor investment decisions we make during periods of volatility. Specifically, there's often a crushing temptation to sell out of out-of-the-money positions for fear of losing more money. This is called panic selling.

Bank of America Merrill Lynch's Savita Subramanian recently did a study demonstrating how panic selling is a losing strategy.

"We compare a buy-and-hold strategy vs. a panic selling strategy from 1960-present," she said. "We assume an investor sells after a 2% down-day and buys back 20 trading days later, provided the market is flat or up at the end of that period."

View photos Buy-and-hold is demonstrably better than panic-selling. (Image: Bank of America Merrill Lynch) More

"This strategy underperforms the market on a cumulative basis since 1960 both overall and during every decade, given the best days typically follow the worst days."

Billionaire investor Warren Buffett is a vocal proponent of this strategy.

"In fact, when we own portions of outstanding businesses with outstanding managements, our favorite holding period is forever," he said in his 1988 letter to Berkshire Hathaway shareholders.

"The money is made in investments by investing, and by owning good companies for long periods of time,” Buffett told CNBC in March. “If they buy good companies, buy them over time, they're going to do fine 10, 20, 30 years from now."

Buy and hold. It's the not-so-secret way rich investors get richer.

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Sam Ro is managing editor at Yahoo Finance.

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