Harvard expert shares her No. 1 'undesirable' trait CEOs see in employees: It's 'a huge red flag for me'

Of the many traits people bring to the workplace, one stands out as an absolute "trust breaker," according to a Harvard career expert.

It's "taking credit for other people's ideas," says Heidi K. Gardner, a professional leadership advisor and distinguished fellow at Harvard Law School. "To me, it signals one of two things," she tells CNBC Make It. "Lack of trustworthiness or lack of competence."

It's unethical to pass off someone else's work or ideas as your own, and it gives off the impression that you don't respect your colleagues, Gardner says: "Maybe they're unable to actually see how much value the people around them bring to their own success. And that inability to appreciate other people's contributions is a huge red flag for me."

You may not even realize you're showing signs of taking credit for the work of others — like accepting your boss's praise for a group project instead of sharing it with your teammates, or presenting an idea that you and a colleague brainstormed together without specifically mentioning their contributions.

This doesn't mean you need to stop collaborating. Teamwork is crucial for any company's success, and by extension, your own success, Gardner says.

Rather, you need to be transparent when an idea isn't your own to avoid coming across as untrustworthy.

"I have to believe that somebody is not a jerk in order to collaborate with them. I have to believe that when they're challenging me or questioning me, they're doing so from a place of genuine constructiveness," Gardner says. "If somebody takes credit for someone else's work or ideas, they are not trustworthy in that sense."

That echoes one of billionaire Warren Buffett's long-held tenets: Trustworthiness is any employee's most valuable trait. In a 1998 speech with MBA students at the University of Florida, Buffett shared the three key qualities he looks for in a potential employee or business partner.

"We look for intelligence, we look for initiative or energy and we look for integrity," he said. "And if they don't have the latter, the first two will kill you. Because if you're going to get someone without integrity, you want them lazy and dumb."

Gardner says the key to success is "smart collaboration," a term she coined to describe when colleagues work together on a task that could have been done alone. It results in increased trust, productivity and quality of work, she says — as long as everyone's transparent about who contributed to the project, that is.

Plagiarizing and being untruthful are "anti-collaborative," and that's the No. 1 trait professionals should steer clear from, says Gardner.

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