When Mark Cuban returns for the eighth season of "Shark Tank" on Friday night, he will be looking for new businesses and products in which to invest his billions of dollars. But he doesn't go after every deal he’s pitched -- even if he thinks it’s a good idea. He says he knows what he's good at, and he sticks to that.

"The idea is the easy part," says Cuban, who joined ABC’s "Shark Tank" in its second season as a guest "Shark" and became a series regular in Season 3. "We’ve all had ideas; everybody you know has had an idea. They get all excited about it. They Google it. They think that nobody’s ever done it because it’s not on Google. Then rather than saying, 'Okay, let me see if I can sell any,' they think, 'Okay, can I raise money?'"

Cuban says that the biggest mistake beginning entrepreneurs make is thinking success is all about raising money. Instead, they should be thinking about sales because no company has ever succeeded without sales.

"I’ll take brains over cash any day. That’s the best way to start a business."

He also says there's nothing wrong with failing: "It doesn’t matter how many times you've failed. You only have to be right one time."

Cuban's deal with the ABC reality series has three more years to run, and he indicates he would extend his stay on "Shark Tank" beyond that as long as he feels the message the show sends out is a positive one.

Of the companies he’s gotten involved with from the show, he says the one thing the successful ones have in common is "they work hard, they work smart and they understand their industries. They understand their management skills and where they’re strong. They know what they don’t know, and they get people to help them where they don’t know."

As for the failures, he attributes them with not being willing to burn the midnight oil.

"They’re not willing to work," he says. "They’re dependent on what I call the Viagra impact of media and PR. You get that little bump that lasts for 20 minutes. Literally, the businesses that I’ve had that suffered the most have been the ones that thought, 'Oh, we got this big bump at "Shark Tank," if only we could just go on more TV shows.' I’m like, 'No, we've got to do the work and get it going.'"

The owner of the Dallas Mavericks, who initially made his fortune through the sale of startups MicroSolutions and Broadcast.com in the 1990s, puts his own money where his mouth is and follows that same advice for his own success.

"I bust my ass and I try to be prepared," says Cuban, who is currently engrossed in the new machine and deep learning areas of technology. "Like literally today, I’ll read three hours, four hours trying to keep up, trying to understand, reading about deep learning, machine learning, trying to stay ahead. And then, I try to combine that with my experience to out-grind the 21-year-olds that are trying to kick my ass."

"Shark Tank" returns for its eighth season on Sept. 23 on ABC.