When I got fired from my first "real job" the manager sat down with me and said. "Michael, I'm really sorry but it's just not working out. Your performance on this last project was pretty bad and we can no longer give you employment with us. It's really nothing personal." It's nothing personal. After going to the restroom and having a fit (and getting some odd stares) I realized what a crock of crap that statement was. To me, it was the most personal thing in the world. I was being told I was not good enough to hold a job there. What could be more personal?
Now, years and many miles more experience later, I realize what the manager was trying to say. He was trying to say "Hey, this is a lousy job doing this firing thing. I'm really not comfortable with it. If you could just do me the favor of not raising a fuss and making it harder for me I would really appreciate it." He was right. It is a incredibly hard job to fire someone. Both sides feel nervous. However, don't minimize the feeling of uncertainty and doubt in the person you are firing by saying "It's nothing personal." Let's face the facts ... you're wrong.