Name change..

I just don't understand how people can just change their names..Like on Facebook sometimes I want to look up someone that I haven't really been in contact for ages and suddenly I can't find the person, I thought maybe he or she deleted me from the friends list. No doubt that is sometimes the case but every once in awhile, I'll stumble upon the person but with a DIFFERENT name! Why would someone do that?! What could compel a person to change his or her name unless it was something so horrible for them to face that they had to resort to such exteme measures? Well, all I can say is, it would pay to be careful of these here-today-gone-tomorrow characters. Worse of all if they're your friend, are you supposed to call them by their old name or new name? Whatever!