One of the best bits of advice I received about teaching in Korea was to maintain a flexible attitude and be prepared for abrupt and last minute changes.
In the States, if a friend/boss/lover was constantly changing plans on you at the last minute, it would be taken as a sign of disrespect. When a person changes the agenda at the last minute, he/she is saying that your time is expendable. Sure, occasionally legitimate problems create unavoidable cancellations, etc., but if someone is constantly making and breaking plans or relying on you to come through at the last minute, they are treating you like a doormat. (Even if they don't realize they are doing this; they could be well-intentioned, lazy, or used to getting their way.)
In Korea, at least in the public school...