Mark Cuban is worth $4.1 billion, according to Forbes, but it wasn't always so clear he'd be successful.

"Nobody had high hopes for me," Cuban said during an episode of ABC's "Shark Tank" in April. "But I was a hustler."

Cuban had some challenging times.

In his 20s, he was sleeping on the floor of a three-bedroom Dallas apartment with six guys. "I had one towel that I stole from a hotel that had holes in it. It was nasty," Cuban said during an Oxford Union Q&A session in 2017. "There were times when I came home, the lights were turned off; I had my credit cards cut, you name it."

And there was a time he couldn't even make the $200 minimum to get a bank account.

But Cuban always found a way to get through the hard times and low points, thanks to his attitude: "S--- happens. You have to get back to work, and you have to go after it, and you have to make the best of it," he said during the Oxford Union Q&A.

Take for example, when he struggled to get financing to buy a car.

"There was a car on the roadway that I kind of liked, and it was obviously abandoned," Cuban said. "I hunted down the bank that had done the financing for it, and said, 'I think I found a car that you financed. Can I have it?' That's how I got a car."

Or take the time Cuban says a receptionist at his then-fledgling first company, MicroSolutions, stole more than $82,000 from the business by forging checks — "$82,000 of the $84,000 we had was gone," Cuban said during the Oxford Union Q&A.

Cuban said he went to the bank to try and get his money back.

"The manager of the bank basically [laughed] me out of his office, telling me that I 'didn't have a pot to piss in.' That I could sue him, or whatever I wanted, but I was out the money."

Cuban remembered waking up some days, "going 'oh my god, is this going to happen,'" questioning if he'd ever achieve success.

But he stayed motivated by being positive and remembering his strengths.

"I was just like, 'I just have to keep on grinding,'" Cuban said during the 2017 Q&A. "And that's always worked out for me. Even when things were the toughest, my attitude has just been enjoy your life, smile, fight your way through it, and remember what you're good at."

According to Cuban, he knew he was good at "tech, selling, working longer hours than everybody else," but more importantly, "I was even better at enjoying what I was doing," he said. "I just kept on reminding myself to enjoy."

"For whatever reason, I never got pissed, I never got upset," Cuban said during the Q&A. "I was just like, 'This is it. I just gotta go. I just gotta do. I just have to keep on grinding.'"

He said he learned that despite doing everything right, like going to college and learning about business, sometimes things just go wrong anyway.

"What I learned from all that was there's always gonna be setbacks....There's always gonna be things you don't anticipate," he said during the Q&A.

"Even when you have every 'i' dotted and every 't' crossed, something is going to go wrong. And when it does, you just have to fight through it and grind through it. Remember what it is that makes you special and what it is that makes you confident to do what you do, and do more of it."

Cuban went on to sell MicroSystems for $6 million in 1990 to CompuServe. Five years later, he and a friend, Todd Wagner, started, which was later acquired by Yahoo in 1999 for $5.7 billion in stock.

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