Mark Cuban, the "Shark Tank" star and billionaire owner of the NBA's Dallas Mavericks, always has his hands in a wide variety of businesses.
Throughout his career, he's made over 120 investments, from large companies like Landmark Theatres to his Three Commas apparel line.
For all of the businesses he's been a part of, he's developed a set of "rules that have been almost infallible," he wrote in his 2013 book, "How to Win at the Sport of Business."
Below, Business Insider has summarized the three he's used "religiously."
1. Understand the difference between adding value and benefiting from a bull market
In the same way that some stock market investors think that they're geniuses when they keep picking stocks that go up, failing to acknowledge that all stocks are doing the same thing, Cuban says, entrepreneurs can fail to recognize that a good deal of their success is because of a fad or trend.
"There is nothing wrong with going along for the ride and making money at it, but it will catch up with you if you lie to yourself and give yourself credit for the ride," he wrote.
Cuban said that he saw this happen with professional sports leagues in the early 2000s. He explained that many team owners became enamored with rising revenues from television-rights deals, crediting it to their own "brilliance."
He said, however, that he and his Mavericks partners recognized that revenues were actually rising because of competition among cable and satellite providers. Cuban couldn't become complacent.
"It's a bigger challenge to recognize that the bull market may end and our programming needs to be of sufficient value to our customers and viewers for it to maintain or continue to increase in value," he wrote.
2. Win the battles you're in before moving on to new ones
Cuban wrote that he had a chance to take Landmark Theatres international, but that any time spent on developing a global presence was time not spent growing its national presence, and so he decided against it.
"You do not have unlimited time and/or attention. You may work 24 hours a day, but those 24 hours spent winning your core business will pay off far more. It might cost you some longer-term upside, but it will allow you to be the best business you can be."
3. Don't drown in opportunity
"If you are adding new things when your core businesses are struggling rather than facing the challenge, you are either running away or giving up," Cuban wrote. "Rarely is either good for a business."
Melissa Carbone, president of horror-attraction company Ten Thirty One Productions, told Business Insider in 2014 that after the $2 million deal she made with Cuban on "Shark Tank" went public, she was flooded with partnership and investment offers, some of which were quite attractive.
Cuban told her to take a step back and not let emotions make her impulsive. She said that she would continually hear Cuban's voice in her head reminding her, "Don't drown in opportunity."