Mark Cuban was only 12 years old when he launched his first side hustle, so he knows what it takes to start a business.

He says there's one thing you need to think about if you want to do it.

Cuban told a group of high school students at Lewisville High School that the key to starting a business is doing things that you can do yourself.

He said that starting with what you know is important.

Cuban said that if it's a product, do something that's easy for you to get and easy for you to sell. You can do the best businesses yourself. Being anentrepreneur is all about that.

Cuban learned to run his own business at a young age, when he was selling garbage bags door to door in a Pittsburgh suburb. He said the proceeds from his collectibles helped pay for his college education.

Cuban used household items and collectibles that were accessible to a kid and sell them for a profit in each of those cases.

He worked as a bartender and taught dance as a college student. Cuban appeared on "Dancing With the Stars" in 2007, where he finished 8th in the competition.

I was a hustling person. I've been selling for a long time. There was always something happening to me. Cuban said during a 2016 episode of "Shark Tank" that he was just his nature.

Cuban tells kids and teenagers to do what he did. He told CNBC Make It in September that they can offer something to friends, family and neighbors.

It is difficult to launch and grow a business. According to data from the U.S. Bureau of Labor Statistics, 20% of new businesses fail in their first year of operation.

Cuban told the students that starting a business isn't as easy as you might think.

"You all would already be doing it and taking my place if it was easy," he said.

It's difficult to find something you can control and do yourself. It is a lot harder to become great at it than it is to be great.

It involves researching your business plan and potential competition, seeking out funding, and creating backup plans to allow for flexibility if you need to adjust on the fly.

Cuban told the students that a world of opportunity can open up for them if they put in the work.

Anything is possible if you are willing to take the initiative and start a business.

CNBC has exclusive rights to the "Shark Tank" show.

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