Barbara Corcoran turned an unpleasant retail experience into a business lesson she still uses today.

Years ago, while shopping with her brother, the millionaire co-star of ABC's "Shark Tank" encountered a sales associate who left a bad taste in her mouth, she said in a recent TikTok video.

"[I was] trying to pay for a tube of mascara. From what I could see, the lady behind that counter had no intention of helping us. She didn't even make eye contact," Corcoran, 74, said. "I said, 'Ma'am, can I please pay for my mascara?' And she ignored me."

Corcoran grew "furious," she said, wanting to give the woman a piece of her mind, until her brother stepped in.

"[He] put his hand over mine and said to me, 'Barbara, hold it. Consider: She's doing the best that she can,'" said Corcoran. "He went on to say, 'You have no idea what she dealt with before she went to work this morning, what her life is like, what's on her plate, what she has to deal with every day."

Today, Corcoran thinks about those words often, she said: "She's doing the best that she can." And they taught her just how crucial empathy is as a soft skill, which she still uses as an investor and CEO.

"[Those] seven simple words made me a much nicer person," Corcoran said.

The power of kindness in business

Being nice doesn't just impact your own outlook: It makes you come across as more relatable and trustworthy to others. Kindness is a valuable leadership trait, according to a 2020 Gallup survey which found that workers have "four universal needs" when it comes to their bosses: trust, compassion, stability and hope.

Mark Cuban, Corcoran's "Shark Tank" co-star, agrees. "I wish somebody would have told me to be nicer," Cuban told the "Bio Eats World" podcast last year, when asked what advice he'd give his younger self. "Because I was always go, go, go ... Ready, fire, aim. Let's go. Let's go faster, faster."

Cuban's lack of kindness, which he called an "underrated" trait, started to negatively impact his employees — so he made a conscious effort to change his ways, he told Vanity Fair in 2018.

"I went through my own metamorphosis, if you will. Early on in my career," said Cuban, adding: "I wouldn't have wanted to do business with me when I was in my 20s [and 30s] ... So I had to change, and I did, and it really paid off."

Kindness is a fairly easy soft skill to develop, experts say. You can start with something simple: During your next conversation or interaction with someone, ask them some questions and really pay attention to their responses.

"Listen both for the words being said and the feeling behind them," psychologist Daniel Goleman told CNBC Make It in 2017. "Respond accordingly, with a sign that you understand, or offer a helpful comment."

"One conversation won't boost your empathy," Goleman added. "But over time, exercising your curiosity and listening closely to others will help you sense more accurately how others think and feel."

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

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