Mark Cuban says a lesson from the former Dallas Mavericks coach taught him to 'face the reality' of what it takes to be successful

• Dallas Mavericks owner Mark Cuban and former head coach Don Nelson had a sometimes fraught relationship, but now Cuban considers him a friend and mentor.
• Cuban said when they were discussing players, Nelson taught him that individuals are the worst evaluators of their own talent.
• From then on, Cuban said, he was aware of his ego's role in a decision, and made it a habit to pass on responsibilities to people who could compensate for his weaknesses.

Anyone who's ever seen Mark Cuban knows that he's proudly outspoken, headstrong, and won't back down from a fight - especially not with President Donald Trump.

But when it comes to making decisions for his businesses for the last couple decades, the billionaire investor explained in his 2011 book "How to Win at the Sport of Business," he's been very cautious of letting his ego lead. And this approach is based on a conversation he had with Don Nelson, the former head coach of his NBA team, the Dallas Mavericks.

Cuban bought the Mavericks in 2000 and retained Nelson as coach through 2005. The two once had a fraught relationship, but by the time Cuban wrote his book, he spoke highly of Nelson and said he "learned a lot" from the coach.

"He told me something early on that opened my eyes," Cuban wrote. "I forget the exact conversation, but we were talking about players, and I asked him why he didn't talk to a specific player about something that was going on. What he said was, 'The worst evaluator of talent is a player trying to evaluate himself.'"

Cuban said that he thought about that line after their conversation and wondered how it applied to his own life, as a highly ambitious entrepreneur and investor. "We don't want to believe that there are things we can't do. We want to believe that if we try hard enough, work long enough and get a little lucky, that the sky is the limit. The problem is that we let our confidence cloud our judgment of what we truly know about ourselves."

When he was 23, for example, he started a software company called MicroSolutions, and his ambition told him that he could handle running every aspect of the business. His talents were marketing and coding, and while he was hopelessly disorganized, he figured that if he just applied his work ethic to becoming a details guy he'd be all set.

Suffice to say, he could not be a master of all and sustain a growing business. After realizing that he was spending more time putting out fires than making new deals, Cuban partnered with a programmer named Martin Woodall, who Cuban said was the most detail-oriented person he had ever met in his life.

Years later, as Cuban thought about Nelson's insight into managing a roster, he understood that the reason he was able to make his first business a success that kicked off his career was because he had overcome the childish idea that willpower alone could overcome any obstacle.

He internalized Nelson's lesson and decided that for all future ventures he would act on his strengths - like marketing and making deals - and work with others who could compensate for his weaknesses - like planning and fine-tuning details.

In a 2015 interview, Cuban told Business Insider that he took this approach with the roughly 40 "Shark Tank" companies he's invested in, in addition to his other ventures. He built a team that can work closely with each of these companies and handle their back office duties, while he can personally vouch for these companies in the media and when negotiating distribution partnerships with companies like Amazon.

When writing about his experience partnering with Woodall, and accepting what his strengths and weaknesses were, Cuban wrote that he would have lost his business if he kept lying to himself.

"Each of us has to face the reality of who we are and what we are," he wrote.