Co-workers have such a big impact on workplace happiness that, in the best-case scenario, people who have a best friend at work are happier, healthier, more engaged and more productive.
Having a work enemy, on the other hand, can make an otherwise fulfilling job unbearable.
Therapist, author and speaker Esther Perel has a new podcast called "How's Work" that invites listeners in on couples' therapy sessions between co-workers. She points to three signs people are working in a toxic work environment: people can't collaborate, there's a lack of trust and peers are overly competitive.
"All that stuff not only creates a negative work culture," Perel tells CNBC Make It, "but it doesn't allow the company to succeed."
Here are Perel's three steps to address a competitive co-worker.
First, Perel suggests really considering whether a competitive colleague is getting ahead at the expense of others, or if they're just good at their job. It's possible their penchant for going above and beyond comes from working to maintain their job and financial security.
"If they compete fairly, they compete," Perel says. "You don't know if they have family somewhere else that they need to support, or if they have a sense of responsibility that is just constantly pushing them to accomplish more .... You don't know."
Perel suggests learning more about what drives the competitive co-worker with a greater sense of empathy and curiosity, rather than one of placing blame.
"It's not a bad idea to just say to them, 'Hey, where does that drive come from?'" Perel suggests.
Robert Sutton, a Stanford professor and organizational psychologist, recommends using a similar mental trick: Establish emotional distance by studying a co-worker the way an anthropologist would. You may be less likely to take what they say or do personally, and you could even gain a better understanding of them and their motives.
A competitive colleague can be toxic when they hide information, put themselves before the team or take ownership of other coworkers' projects. In this situation, it may be worth asking fellow colleagues whether they feel similarly about an individual's behavior.
Perel draws on the work of psychologist Howard Markman and points to three main sources of conflict she sees in the workplace: power and control (Who has the decision-making power?), trust (Who has my back?), and respect and recognition (Am I valued?).
Perel says it's common for co-workers to lose trust in each other when there's a competitive co-worker in the mix. While this kind of behavior may feel personal, it becomes a workplace issue when colleagues are unable to get their work done efficiently.
"Anything that destroys the basic foundation of trust is going to be a problem," Perel says.
If multiple people on a team feel this way, it may be time to escalate the concern to a manager.
When raising the issue with a supervisor, it's best to come prepared with your own recommendations about how to improve the situation.
"So you've also come with a clear request," Perel says. "You don't just come with the criticism."
For example, it may be helpful for the supervisor to be more clear in delegating responsibilities, timelines and expectations among a group, so individuals are aware of who is in charge of certain tasks. That could help eliminate a competitive co-worker overstepping and taking credit for someone else's responsibilities.
It can also be helpful to ask a supervisor for more context as to why the competitive co-worker may act in a certain way. It's possible they may be facing pressure from external clients you're not aware of, for example, or they're in the process of switching departments and are in a crunch to deliver projects by a deadline.
"All of that is going to determine how you want to deal with this person's competitiveness," Perel says.
Management author and CNBC contributor Suzy Welch agrees that there's a certain point where it's necessary to escalate the discussion to a manager.
"You can — and you should — go to your boss if a colleague is making you feel nervous, threatened, manipulated or undermined," she previously told CNBC Make It. "And definitely go to your boss if you feel a colleague is a danger to him or herself."
And remember, it's in an employer's best interest to provide a safe and productive work environment for their employees, Perel says.
"I think our work economy wants us to experience purpose and meaning and joy in the workplace," she says. "And all of those things require good relationships. No amount of purpose or money or even free food will ever compensate for a poisonous relationship in the workplace."
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