In my over 15 years of air travel, this had never happened before (until this incident). I may consider myself lucky in this regard, but I always thought that when you had the boarding pass and sat on your seat - you were "safe." Only in an extreme circumstance, could you be asked to be removed from your seat (and with some kind of compensation). I don't believe this was an "emergency" that required me to give up my seat. Also, there were other people who got on the plane from standby list after me (ie: I was not the last person cleared the standby list). One of these people could be asked to volunteer to give up their seat.