38-year-old millionaire shares the 'worst financial decision' he's ever made

Chris Reining mastered his money from an impressively young age. He built a $1 million portfolio by age 35 and retired at 37.

Of course, no one gets everything right. Reining regrets the $200,000 condo he bought at age 26.

The now 38-year-old retired millionaire was smart about the purchase — he saved enough to put 20 percent down and has since paid off the mortgage — but still calls it "the worst financial decision I've ever made."

Reining, who is based in Madison, Wisc., bought it for the wrong reasons, he writes on his blog: "to show everyone I was successfully navigating adulthood" and "to achieve the American Dream of buying a house."

At the time, it seemed like the natural step to take after getting a college degree and landing a stable job. "With home buying, a lot of people don't question it — and I didn't question it either," Reining tells CNBC. "I just bought it because I thought, 'Oh, everyone buys a house. That's what you want to do, right?'"

While many people consider real estate an asset or an investment, at the end of the day, owning a home takes money out of your pocket, he notes: Mortgage payments, property taxes, maintenance and repairs are just a few of the many expenses that come with home-ownership.

Plus, owning a home comes with what Reining calls "soft costs": your time and reduced flexibility.

He's not the only one to challenge the notion that a home is an asset. Personal finance author Robert Kiyosaki and self-made millionaire Grant Cardone say homes should be considered a liability . "Never think a home is a way to create financial freedom," Cardone writes on his blog.

"A house should be looked at as an expense, not an investment and merely a place to live."

Of course, depending on your individual situation, you may be better off buying than renting . Crunch the numbers and weigh the pros and cons of home-ownership before committing. And, as Cathy Derus, CPA and founder of Brightwater Financial, advises, " be intentional with your purchase ." Don't commit for the wrong reasons.

At the end of the day, "if people want to buy a house, buy a house," says Reining. "But don't buy a house and think that it's going to be, or end up being, the best investment you're ever going to make."

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