Millionaires may not be as uncommon as you think.

There are more than 20 million people in the U.S. with enough assets to fit the definition, according to a 2020 study by Credit Suisse.

Chris Hogan, radio host and author of the book "Everyday Millionaires," surveyed more than 10,000 of those wealthy individuals to figure out their secret to success.

Hogan quickly learned that most millionaires aren't the jet-setters you see on television.

"These are regular, hardworking, everyday people. They're not flashy," Hogan said. Most of them accumulated their wealth over time by making wise decisions, according to Hogan.

And having a particular mindset almost universally contributed to their success, Hogan said. He found that around 97% of millionaires surveyed believed they were in control of their own destiny.

That is much higher than the 55% of the general population Hogan found to hold the same opinion.

Check out this video to see the other four beliefs and practices that more than 90% of millionaires apply to their money.

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Disclosure: NBCUniversal and Comcast Ventures are investors in Acorns.