Kevin O'Leary runs several companies that bear his name: wine business O'Leary Fine Wines, private equity firm O'Leary Ventures and financial company O'Shares Investments. He's also famous as a judge on ABC's "Shark Tank," through which he's invested in businesses like Plated — a meal delivery company that .

But it took years for O'Leary to succeed in business. And that struggle taught him something important.