Can I fire an employee for her negative attitude?

I have a mentor at work who is very negative about the company — she kind of brings me down, and I don't know how to get out of the relationship. Any advice?

Breaking up is harder to do at work than in our personal lives, and it isn't as easy to move on since you may have to continue seeing each other — and fear that the split might have career implications. But it doesn't have to be that way: You can try adopting a reverse mentoring approach, and address the issue to help your mentor become more self-aware about how they are presenting themselves — and how it isn't constructive or helpful for their own career and anyone they manage (or mentor!). If that doesn't work, or if you are uncomfortable with that approach, your other alternative is to make less time for your mentor, and don't initiate any additional meetings. Soon enough, the relationship will fizzle out, just like with personal relationships — hopefully without the drama and heartbreak! Good luck.

I have an employee who does good work, but can dial up the stress factor when things are a little intense. If I wanted to fire her, is that a legitimate reason?

Emotions are contagious, and can dictate the culture of a department. Negative attitudes can only hurt productivity and culture; they can't help. That said, you don't need to have a staff of smiling Pollyannas — nor would you want one, for that matter, because anyone who is too happy all the time will get on your nerves just as much! A healthy balance of New York cynicism and a can-do, make-it-happen attitude works really well. So if you feel someone's demeanor is hurting the business or culture more than their work output is adding value, it is a valid reason to address the issue — and if the person can't or won't change, it's a valid reason for you to make a change.