You know who they are – the top performer whose rare talent took forever to find and whose skillset was the missing piece to your team’s performance puzzle. These employees can be dream (and often expensive) hires for any organization – that is, until they become nightmares. At times, these employees can drive powerful results for your business while leaving everyone else in their wake.

There was a time at Walmart, Inc. where I had to face this exact dilemma. I hired a brilliant woman who had a skillset the business really needed. She had created a simple but highly relevant member strategy for Sam’s Club. Due to her brilliance, we were quickly becoming more relevant and top of mind to our club members and her strategy was extremely successful. She was incredibly productive and reported directly to me.

However, I was so focused on her skills and the results she brought to the table that I overlooked two years of her mistreating her team. Eventually, I learned she had demanded so much from her team, she would talk down to them in front of other associates and really made them feel marginalized. Her team was full of good, hardworking people who played a key role in the company’s success. However, her behavior toward them was extremely toxic and destructive.

When someone is delivering strong results, he or she seems invaluable, and it may be hard to see any negatives that are tagging along with that success. In my case, I was starving for the right mix of technical strategy and consumer skills that would supplement my ability to sell it inside the organization.

I had to make the tough judgment call. Despite her brilliant skills and strong strategy, I had to ensure my associates were treated with dignity and respect.

The toughest call to make happens when someone is excelling in their role but failing their team. And when you have to make that hard-right decision to change direction, you are sending the message that results are not more important than how you achieve them.

Here’s what to do if your top performer is killing your company culture and how to keep things from going too far.

Assess the damage: There’s a difference between someone who is toxic and someone who is difficult — whose behavior is thorny and vindictive versus demanding and taxing. Are they belittling people in public? Demeaning people in a way that causes them to lose self-confidence? Are they commandeering projects or making threats to others? If one of these behaviors sounds familiar, you would be wise to pay close attention and address it.

Avoid tolerance creep: I’ve seen firsthand how tolerance creep can threaten any organization. This is when leaders turn their heads and accept gray-area behavior from those around them. They find themselves saying, “Just this time” or, “It’s not really against the rules” or, “it might be fuzzy, but it’s OK.” This behavior can cause irreparable damage over time and will result in a longer season of regaining trust back from your team.

The best way to combat tolerance creep is by knowing your bright lines. Like traveling on a highway, it’s important to stay in your lane—not crossing the bright-yellow lines. Take a step back and look at the situation with a neutral mentality. What will you stand for? What are the things that deeply motivate you and inspire you to do your best work? What are your non-negotiables? I cannot overemphasize the importance of knowing your bright lines – they are absolutely essential for navigating the gray areas of leadership.

Use your voice: You have to find your voice and share your thoughts in a proactive way. There’s a difference between bellyaching and addressing a pressing leadership issue in a concrete way. This step isn’t reserved for the C-suite either. Those who are at the front lines of an organization can often play an essential role as the first domino to fall — shedding light on what’s really happening on the ground floor.

Take action: I eventually had to make the tough call of firing my top performer. And although firing someone is never a decision you should make lightly, it’s important to remember other talent does exist. Your hire might seem like the only unicorn in the world, but in reality, they’re simply a horse with a shiny tail. There’s more to discover if you look closely. You’ll also experience an even bigger win if that person is a strong fit for your company culture.

Set the tone: After firing that employee, we had to set the tone for the rest of the team. We had to make sure they knew that success wasn’t just about what we did to achieve results but also how we go about achieving them. We wanted to set a tone of centeredness and excellence that would reaffirm and build trust within the team for years to come.

Addressing toxic performance syndrome is the hardest to address. You won’t always feel like you’re doing the right thing and sometimes the lines will gray. Still, you have to stand firm the minute that behavior crosses the line and make a decision that is healthy for both you and your team. If not, you risk losing the integrity of your organization’s core values.

I’ll leave you with this last thought. If not you, then who? I’m a firm believer that you should leave an organization better than when you joined. A company should thrive in new ways simply because you were there and made a meaningful impact. Someone has to make the first move, otherwise, a toxic scenario could turn into a tree that falls in the forest – did it really happen?