Before Sean Conlon built his multimillion dollar fortune selling real estate, he'd been "knocked down about a hundred times," he tells CNBC.

Conlon, an Irish immigrant who came to the states with $500 in his pocket, started as a janitor before getting into real estate in 1993. "I'm brand new in the business," he recalls, "and I had a couple call and they want to see properties."

They were "your classic buyer," says Conlon. "They like nothing. … But then I saw a 'for sale by owner,' and I showed it to them naively." The guy selling the property was a broker and told Conlon he'd get paid a commission if the couple ended up buying it.

The couple abruptly stopped calling Conlon back, he tells CNBC: "Eventually, the husband calls and he says, 'We're just not dealing with you. We don't think you know what you're doing. You're not professional enough,' so I was devastated."

One month later, Conlon was driving to work and saw a moving truck outside of the "for sale by owner" home. Sure enough, the couple was moving in.

"I call the owner and he's like, 'Hey kid, I'm a big-time broker. I'm busy. I don't have time to deal with you,'" says Conlon. "That was an incredible lesson. ... I thought about giving up, but I didn't."

Nor did he think about getting revenge, but he had an opportunity anyway, years later, in 1999. "I'd lent a guy $900,000 and he was doing a $4 million deal," says the real estate mogul, who now hosts CNBC's "The Deed: Chicago." "We're getting to the closing and I have to sign off on the payoff. I look at the brokerage commission — it's $120,000 — and I look at the name, and it was the guy who had owned the house."

Conlon called him up: "And he's like, 'Oh my god, it's so amazing to get to speak to you. You're the biggest broker in the country.' I said, 'I'm calling you on something else. I'm calling you on Sean Conlon circa 1993. I sold your house and you [cheat] me out of the commission. Isn't life an amazing thing? So we're going to shave your commission a little bit.'"

He shaved it by $80,000. "You don't always get the story to end up that beautifully," says Conlon, "but that one did."

The moral of the story, he tells CNBC, is to not "get consumed when somebody screws you over. … Don't put all your energy into trying to get them back. Keep winning. Get up and go back in there every day. And you know what? You just might get a shot at your enemy at some point."

Watch Sean Conlon in CNBC's "The Deed: Chicago," on Wednesdays 10:00 PM Eastern.

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