Billionaire entrepreneur Mark Cuban is famously blunt. So, when Inc. asked him in a 2017 interview to share his best money advice, the star of ABC's "Shark Tank" and the owner of the Dallas Mavericks didn't mince words. "From my dad," he said. "Don't use credit cards." The one thing he wishes he had known about money in his 20s, he told Business Insider in 2014, is "that credit cards are the worst investment that you can make. That the money I save on interest by not having debt is better than any return I could possibly get by investing that money in the stock market. "I thought I would be a stock market genius. Until I wasn't. I should have paid off my cards every 30 days."

Mark Cuban John Lamparski | Getty Images

Thanks to exorbitant interest — the typical credit card charges 16.4 percent — not paying off your balance in full each month can end up costing a fortune in the long run. Unfortunately, many people fall into this habit and don't or can't pay off their balances. Credit card companies make it incredibly easy to spend money that you don't have: Most cards only require you to pay one percent to three percent of your balance each month, and that can be a tempting option if your budget is tight. Cuban's solution is to simply ditch the plastic, and he's not the only rich person who benefits from living that way. Comedian and self-made millionaire Jay Leno prefers cash over credit, too. "I barely use credit cards," he tells CNBC. "I don't carry any debt. I don't write checks at the end of the month for anything." And that includes a mortgage, Leno says: "I didn't buy my house until I had cash. "When you own something and you don't have to write checks every month, you're just better off."