The Corner Seat...

In my office in my room there is a corner seat. The first day I joined it was empty. Second day it had an occupant. She preferred the corner seat because it covered her from all sides. It was her territory.  She was happy. The corner seat indeed covered her. She hid behind it from the eyes of outsider. And one day she was gone. She left the office never to return. The corner seat was empty again. I looked at corner seat temping me to sit. But I looked away. Soon came another girl. She chose the corner seat.  The proud corner seat had yet another occupant. Days passed by all bright and right. Then one day she left without a sigh. The corner seat was empty yet again. What is the mystery behind the history of the corner seat???