Sometimes, bosses have to make difficult decisions, which is why Louie Bernstein once fired his best salesperson.

In 1986, the then 34-year-old founded an Atlanta-based IT training company called MindIQ. A few years later, he hired someone who quickly became his top salesperson, Bernstein told LinkedIn's "Catalyst" video series last week.

"I interviewed this one woman who presented herself great. She had a good personality — so I thought — and I ended up making her an offer ... She just started making sales right away," said Bernstein, now a 72-year-old sales executive and leadership consultant.

Once he started working with her, he discovered that she lacked a key soft skill, and without it, she was a nightmare to work with, he said: coachability.

"In the end, I felt like we had cancer and I was the surgeon that needed to cut it out to save the company," Bernstein wrote in a 2022 LinkedIn post. "Shortly after her departure, sales picked up along with the attitude and harmony of the office."

You can't 'outsource' hard choices

Bernstein's salesperson would often boast about her performance, and how her co-workers weren't on her level, he wrote. This left a bad taste in her peers' mouths, and when Bernstein caught wind of her behavior, he advised her to change. She refused, but because of her stellar sales record, he swept it under the rug, he said.

"I had ignored the toxic traits of my top salesperson," said Bernstein. "The red flag started going up, but I still gave her the benefit of the doubt."

When Bernstein's employees grew dissatisfied with each other, he told them to work out their differences on their own, instead of handling the issue himself, he added. The result: an explosive argument with yelling and crying, said Bernstein.

The ordeal was the push he needed to fire the employee and learn the importance of taking control as a boss, he said: "There comes a point when the manager has to realize they have to make the hard decisions. You can't outsource them."

After that, Bernstein said, he started asking job candidates questions like "How well did you work with someone when you encountered a problem in the middle of a project?" and "How do you deal with people you don't agree with?" — and taking their responses seriously.

The type of employee you never want to be

Acting like you're owed something — or, in this case, like you're above reproach and constructive criticism — is a major red flag in any workplace, workplace culture expert Tom Gimbel told CNBC Make It in April.

But plenty of people struggle to receive tough feedback gracefully. If you fall into that category, leadership and mental toughness expert Scott Mautz has a few tips for you.

First, focus solely on managing your reaction and trying to avoid an initial outburst. "Take a breath and focus on that breath [and] name what you're feeling so that the emotions lose some of their hold over you," Mautz wrote for CNBC Make It last month.

"Then you can listen and ask questions to fully understand the feedback," wrote Mautz. "It's not about minimizing your emotions, it's about managing them ... Mentally strong people manage their emotions so they can respond with intention.

Finally, try to separate the ego-bruising part of the feedback from anything that could be interpreted as genuine advice meant to improve your performance. The more you can hold on to the helpful criticism and filter out the fluff, the more you'll show that you're coachable and able to incorporate feedback into your job performance, Mautz wrote.

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