Mark Cuban is known for being a successful businessman.

The 61-year-old entrepreneur owns the NBA’s Dallas Mavericks, has stakes in numerous companies, is one of the judges on ABC's "Shark Tank" and is estimated to be worth $4.3 billion, according to Forbes.

But before he made it big, Cuban could barely hold down a job.

"I had quit or been fired from three straight jobs," he said on an episode of "Shark Tank," according to a 2017 CNBC report.

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Cuban graduated from Indiana University in 1981 and went to work at Mellon Bank in Pittsburgh, Pa., converting the paper processes to the computer system, he wrote in a 2013 essay in Forbes.

While he was there, he started a newsletter and a happy hour group where younger employees could talk with senior executives. However, his boss didn't like the initiative.

"He told me I was never to go over him or around him, or he'd crush me," he wrote in the Forbes essay. "I knew then it was time to get out of there."

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From there, Cuban went to work at a TV repair franchise called Tronics 2000 in Indiana but eventually headed to Dallas, where he moved into a three-bedroom apartment with five other people.

He was 24-years-old and had no money, according to the CNBC report. He decided to start his own business selling powdered milk, according to Entrepreneur magazine.

That venture didn't last long.

"I honestly thought it would make a killer business and it lasted minutes," Cuban reportedly said about the business.

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After that, he got a job at a PC software company called Your Business Software, making $18,000 a year plus commission, he wrote in the Forbes essay.

But he didn't last long there, either.

"About nine months in, I got an opportunity to make a $15,000 sale," he wrote. "I was going to make a $1,500 commission, which was enormous. It would have allowed me to move out of the apartment and maybe have a bed."

He told his boss, the CEO of the company, that he was going to close the deal during his opening shift, but that he had someone covering for him. But his boss told him not to go.

He did it anyway, thinking his boss would be impressed with the check.

"Instead, when I came back to the office, he fired me on the spot," Cuban wrote. "I had disobeyed him."