Billionaires and CEOs have something in common with the rest of us: They didn't know everything in their 20s.

The people who start and run awesome companies, write best-sellers, and become household names haven't always known what was best for their money. How do we know? We asked them.

From investor Mark Cuban, who laments his misuse of credit cards, to TOMS founder Blake Mycoskie, who cautions against chasing money, keep reading to find out how investors, CEOs, authors, and other highly successful people answered the question: What do you wish you'd known about money in your 20s?