Entrepreneur Kevin O’Leary never feels guilty about the advice he metes out on ABC’s “Shark Tank,” though it’s often a crushing disappointment to the inventor.

Known as “Mr. Wonderful” for his dismissive attitude, O’Leary explains there’s a reason for that.

“Years ago — and I didn’t understand the value of what she said to me — my mother said to me once, when I think I was 14, ‘Kevin, always tell the truth and you’ll never have to remember what you said.’

“I didn’t put any weight on it then,” he says. “But as life went on and I started doing that and practicing that — it’s not a comfortable place because a lot of people don’t want to hear the truth, particularly in business when you're telling them their idea has no merit, they’re going to go bankrupt and waste their family’s money — it’s hard,” he says.

“But she was right. The truth in the end is the best path because you don’t get caught in a lie later. And you damage relationships so much by lying to people and I think, yeah, I get named as ‘the mean guy’ but I’m the only guy who tells the truth.”

O’Leary is telling the truth again in a new venture — this time he’s holding court on CNBC’s new show, “Money Court.” Along with former judge Ada Pozo and trial attorney Katie Phang, O’Leary presides over a litany of financial disagreements — from family disputes to company collapses. What he says, goes on this show. And that’s not always welcome.

“I know many people don’t like me,” he shrugs, “but many people trust me; they hate me, but trust me. What a weird dynamic that is! When it comes to ‘Money Court,’ they’re willing to say, ‘I don’t like that guy, but I'm going to do what he says and trust him.’ It’s a good place to be.”

While truth-telling may be a good place to be in business, O’Leary says his rule applies to domestic life, like marriage, too. “I wrote a book on it called ‘Men, Women & Money.’ Here’s the best analogy: When you get involved in a romantic relationship — I draw the analogy to a business partnership, too — so everybody gets tempted, particularly in young relationships, and they cheat.

“That happens a lot. And you have a decision to make the next morning. Your decision is, ‘Do I tell the truth now, or do I live in the lie in the hope that it’s never discovered?’”

O’Leary says the chances are that the transgression will be discovered. “Ninety-nine percent of the time, you will be found in your deceit,” he insists.

“It will happen one way or another. It’s just karma. When that occurs, you will lose. Whatever your equity was in that relationship, you will lose 50% of it, and you will never get it back. Never,” he says.

Had the truth been told, it would be a different outcome, he thinks. “Had you said that you honor your relationship so much and you felt bad about what you did, and for whatever reason you did it, you don’t lose 50% of the equity.

In 1986, O’Leary co-founded a software company in his native Canada that he eventually sold for millions. And while he’s known for his savvy business acumen, he’s made his share of mistakes, he admits.

“I’ve had many great successes and many catastrophic failures. And I think every investor does,” says the 67-year-old.

“I remember one in particular that I’ve never forgotten because it was a mistake I did to myself. I’d given $250,000 to a good friend of mine for a deal that he thought he could make work. I did it for emotional reasons, which was a mistake in the first place, and then six months later, when it was on the brink of bankruptcy, he asked me for another $250,000 to get him through the hurdle.

“And my gut told me: ‘Don’t do it. Write off the first $250,000, forget about it, move on. Try and keep the relationship as a friendship not as a business partnership.’ And I didn’t do that.”

O’Leary forked over another $250,000 to his friend. “Six weeks later, he was bankrupt, so I lost half a million dollars. I was so pissed at myself for just not trusting my own instinct — which is really experience. I’ve never let emotions get involved in business ever again. I don’t care what the appeal is, I just won't do it. My instinct is what I trust, and I'm more often right than not.”

While he’s best known in the competitive financial world, O’Leary says his dream is to improve his facility with the guitar. “This is a skill that you can never stop learning,” he says.

“It’s about time and practice. What I do now is I have multiple guitars in all of my homes and all of my locations in hotels in New York. When I pull into my hotel, they take the amp, the guitar and put it in my room. I leave them all over the country. And I try and practice so I can be better. That’s the whole idea,” he says.

“You realize it doesn’t matter how much money you have, it’s irrelevant as to how good a guitarist you are. It has nothing to do with each other.”