Kevin O'Leary is most famously known for his role on ABC's Shark Tank, the television show where entrepreneurs pitch their business ideas to investors in hopes that they will receive a life-changing offer. Not just anybody can be a 'Shark'—you need to have a keen eye for business, an expert understanding of the market, and, most importantly, the funds to make dreams come true.

O'Leary has it all. He built his fortune from founding SoftKey Software Products, which he later sold to Mattel. Now, he serves as chairman of O'Shares Investment Advisers and Beanstox. In an interview with Business Insider, O'Leary shared the one piece of financial advice that he has followed for years, and it came from none other than his own mom.

When he was young, she would tell him to always save 10% of his money, whether it was a gift from his grandparents or his earnings from mowing people's lawns or working at the ice cream shop. Despite being told this early on, O'Leary said it really stuck with him. In fact, he said continues that very saving habit today, and it has even influenced many of his major investment decisions.

"It's a mantra of mine, that everybody can save because there's just so much stuff you buy that you don't need. And if you put that money into the market, which generally is giving 6% to 8% a year for the last 100 years, you'll end up quite wealthy when you retire. It's the secret to success," O'Leary said.

With regards to Shark Tank, O'Leary's mother gave him another tip for success on the show: "Always tell the truth and you'll never remember what you said." He explained that people need to be told hard truths sometimes, no matter how difficult it is to be the bearer of those truths.

"They call me the mean shark, but that's not true. I'm the truthful shark."

Lastly, he ended the interview with his own nugget of wisdom. His best career advice for young individuals is to have a balance. While he agrees that it's important to focus on one's business and investments, a person can never live a balanced life if that's all he or she ever focuses on. Part of that balance involves making sure you take care of yourself.

"If you're healthy and energetic and you have balance in your life, you can live a long time. Great advice again from my mother, she really focused on that and taught me about food and exercise. And it's funny how you go back later in life and think, "I should have listened more to what she was saying because she was 100% right."