Entrepreneur Mark Cuban owns the Dallas Mavericks, stars on ABC's "Shark Tank" and is worth an estimated $3.9 billion. If you ask the businessman what it takes to succeed, though, he doesn't just point to work ethic and negotiation skills.

As Cuban told Vanity Fair in a 2018 interview with the "Shark Tank" cast, a simple skill that anyone can develop can go a long way: "One of the most underrated skills in business right now is being nice. Nice sells."

He continued: "I went through my own metamorphosis, if you will. Early on in my career, I was like bam, bam, bam, bam, bam — I might curse. I might get mad. And then I just got to the point — I wouldn't have wanted to do business with me when I was in my 20s.

"And so I had to change, and I did, and it really paid off."

Science backs his claim that soft skills can boost your career: Studies show that a high level of emotional intelligence, or EQ, can make you wealthy and successful.

As global career development expert Soulaima Gourani tells CNBC Make It, what makes you most valuable is your ability to cooperate and connect with others: "A lot of jobs are going to disappear, but the thing that we will always have that is more important is your emotional intelligence." She defines that as having a "good understanding of yourself, self-control, empathy and a natural understanding of people's decisions, needs and desires."

She adds: "If you can handle people's diversity — people of a different age, different personalities, or educational backgrounds, for example — and you can handle the conflict that comes with that, you will be the highest paid, most valuable employee in the company."

To put it bluntly, at the end of the day, "people hate dealing with people who are jerks," Cuban wrote in a 2014 Entrepreneur article. "It's always easier to be nice than to be a jerk. Don't be a jerk."

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