Employee Motivation

All right, so I blew my cool today at work. I mean the day started OK, the kids co-operated in the morning, it was a bright sunny day and I had completed a task by 10am that I thought might take more than half the day. Then it happened. While discussing the financials of a project I'm involved in, I questioned one of my employees on a number that she is responsible for and is a key component of the assumptions I am working under. My questions was, I thought, fairly innocent and simple: while looking ata spreadhseet I asked "How did you come up with this number?" Her body immediately took a defensive stance and without saying anything she left my office muttering about the spreadsheet we were looking at. She came back about five minutes later, still defensive as her tone of voice indicated, and started asking me why I was looking at a particular spreadsheet and that I should always come to her when I need a number and she started going on about how hard it was to update the data and how I didn't understand what I was looking at and on and on. I listened and tried at the end (I thought) of her rant to give her some guidance on how to prepare and update the data with an example but she kept interrupting. No, not interrupting but not even listening to me. Every time I would try to start a sentence she would continue to speak, continue to complain how I didn't understand the difficulty she was under and on and on. Now, usually, I let her go on until she tires herself out and start my speach. To her credit, when she actually stops to listen she does retain what she's been told and usually does an excellent job. But today I grew so impatient because I could tell she felt I was accusing her of something and she simply would not stop talking. I finally raised my voice and talked over her. And boy did I raise my voice and ket her have it. She looked shocked but she listened. She even cried a little. Now I'm not exactly proud of making her cry but she needed the yelling. After a few minutes of me blowing my top we were able to get on the same page and have a productive discussion and eventually uncovered what I needed to uncover. She actually aplogized to me for not letting me talk and I aplogized for yelling. Later my boss, who had heard everything as his office was right next to mine, came in said that I was absolutely correct in everything I said and you sometimes do need to use different methods with certain people and that might even include yelling. I probably shouldn't have lost my cool but man was she ever annoying. Whew, just had to get that off my chest.