This story is part of the Behind the Desk series, where CNBC Make It gets personal with successful business executives to find out everything from how they got to where they are to what makes them get out of bed in the morning to their daily routines

There's a lot you might not know about Kevin O'Leary.

Maybe you didn't know the star investor on ABC's "Shark Tank" grew up dyslexic. Or, maybe you didn't know he got his financial chops from his Lebanese mother, whom he says "kept a secret [bank] account from both of her husbands, her whole life."

You might think he's mean, based largely on his television persona. O'Leary disputes that assertion. "People call me mean. I don't think I'm mean," O'Leary, 67, tells CNBC Make It.

Instead, O'Leary says, he's simply following advice he received as a teenager from his late mother Georgette: Never tell a lie, and you'll never have to remember what you said. "In other words, I tell it the way I see it," he says.

O'Leary credits that honesty, even when it hurts, to his success — dating back to his first entrepreneurial endeavor, a company called Softkey Software that he launched from his Toronto basement in 1986. The company later morphed into the educational software firm The Learning Company, which O'Leary and his co-founders sold to Mattel for $4.2 billion in 1999.

Since then, O'Leary has invested in and advised a slew of businesses, from crowdfunding start-up StartEngine to "Shark Tank" companies like DrainWig and Wicked Good Cupcakes. He's also a bestselling author who serves as the chairman of O'Shares ETFs.

The road to get there has been far from easy, he says — from losing his dad at age seven to making mulitiple business mistakes along the way. Here, O'Leary talks about growing up with dyslexia, the moment that made him a lifelong entrepreneur and why he really isn't that mean.

On growing up with dyslexia: 'I didn't really have a disability. I had a superpower'

I had serious dyslexia when I was young. I started to fall behind in school in math and reading skills. But I was very fortunate to get into an experimental program at McGill University.

It was run by two professors, Sam Rabinovich and Marjorie Golick, who are now legendary in dyslexia. They taught me that I didn't really have a disability. I had a superpower.

At that age, the whole idea was to reduce my anxiety — because I could actually read a book upside down in the mirror in front of my class. That's one of the attributes certain dyslexics have. Once I showed them that I can do that, that's how I started reading until it resolved itself.

There are lots of examples of dyslexics that have done well in business, later. But they have to overcome the attributes.

On the moment that made him an entrepreneur: 'For me, it was getting fired ... as an ice cream scooper'

Every time I talk to successful entrepreneurs, there's one moment in their lives that changes their direction. For me, it was getting fired at Magoo's Ice Cream Parlour as an ice cream scooper.

It was the first and only job I ever had. I got fired on the first day because I didn't understand the idea of the employee-employer relationship. I only took the job because I wanted to be close to this girl that I was interested in. She was working at the shoe store across the mall.

On the first day on the job, the owner said, "The floor is completely covered with gum. You've got to scrape it off before you leave, and you have to do that every day." I said, "I can't do that." I was worried that the girl across the mall was gonna see me on my knees, and that was bad for my brand. So she fired me, and that was the last job I ever had.

I learned that I can't work for anybody. I have to control my own destiny. I'm not against [the concept of] being an employee, but I can't [personally] do it. That was the direction of my ambition from that day on.

On the source of his financial chops: 'My mother ... was very hardcore about making sure she could take care of herself and her family'

I think it has a lot to do with my Lebanese mother. In the Lebanese family hierarchy, matriarchs run the show and so did her grandmother. They set the tone for the family.

My mother was fiercely independent. She wanted her own financial pillar for herself. I think I inherited that from her: She was very hardcore about making sure she could take care of herself and her family.

She wasn't an analyst or anything. But when she passed away, the executor called me and said, "You gotta get down here. Your mother died a very wealthy woman."

I had no idea that she kept a secret account from both of her husbands, her whole life. That's just how she worked.

On the best advice he ever received: 'Never tell a lie'

I go back to something my mother taught me when I was a teenager: "Never tell a lie, and you'll never have to remember what you said." I wasn't practicing this back then, but I've certainly come to realize the merit of it now.

I tell it the way I see it. Many people don't agree with me, but it's the ones that don't agree with me who get into dialogue and debate, and I think that's very healthy.

I know that gets me the "mean" tag on "Shark Tank." But when a deal is really crappy, you should tell them the truth. Sometimes, that's very hard, but I find that people can smell bull---- a mile away on social media. You've got to be honest, and I think that engages [people].

I have a very large [following], and I'm very interested in what they think. I quiz them all the time when I want to decide on something. As long as you don't bull---- them, they'll be with you for life.

On the biggest misconception about him: 'I don't think I'm mean'

That persona from "Shark Tank" is actually me in business mode. I don't think you can be one person on TV and a different person [in real life]. I'm not an actor.

If people don't like the truth, I can't help them — it's still the truth. I think I do people a great service by not trying to save their feelings.

This happens all the time on "Shark Tank," with Barbara [Corcoran] or Lori [Greiner] beside me saying, "I won't invest but you keep doing what you're doing." And I say, "Why are you telling them that? This is a really bad idea. You're cursing them and giving them hope for something that's worthless."

And for that, I get a bad rap. People call me mean. I don't think I'm mean.

This interview has been edited for length and clarity.

Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank."

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