What is wrong with me?

I have to thank my Heavenly Father for outpouring of eye opening experiences I've had lately. Tonight I am feeling rather low about my recent behavior to a new employee at my job. As some of you know I was promoted to a management position at US Bank within the past month. I work at a fairly busy downtown branch, and due to various reasons we've been very short staffed. We recently hired a new teller. I had misgivings about her because of previous runins with her. She came off as the type of personality I clash with. So from the moment she started working with me, I had it out for her. She spent almost 2 weeks on her web based training that should've only taken 3 days. When you try to explain things to her she interjects and never lets you finish saying what you have to say.

My husband says I tend to have very high expectations of myself and others, and when those expectations aren't met, I come down very hard not just on myself but others. He's said this more times than I can count, yet I don't think I ever really HEARD him. I was having less and less patience for my new teller because she wasn't picking up on things as quickly as I had hoped. From my perspective I felt she didn't take it seriously, and all in all it was hurting us more to have her there than helping us. I take my job seriously, but maybe I've taken it too seriously.

This new employee broke into tears today telling me she didn't appreciate the way I treated her. She told me I was belittling her, and talking down to her and she knew that I was obviously very frustrated with her and that she was going to put in her resignation tomorrow. AGH. I was shocked by her outburst. My first reaction was to become defensive and point out everything she did that caused me to treat her this way (as if that would justify my behavior). I realized in that moment that I had hurt somoene because of my careless acts. Who do I think I am that I can treat someone this way? Sure, I didn't realize I had come off as badly as she portrayed, but I knew in my heart I surely wasn't innocent. I apologized and we talked a little bit, but I know things are still unsettled. It appalls me that I could actually be so cruel and it took a confrontation for me to stop and care. Patience was never a strong virtue of mine, but I'm disgusted by what I've allowed myself to become. Even worse, I'M supposed to be an EXAMPLE. Most of all I'm ashamed. In the grand scheme of the things, all the things that upset me about her truly don't matter. I don't know what's going to happen... but something's gotta change. And I'm guessing that change has to come from me.