UGH, Some People

Ok, I need to vent for a second....Why is it that when you plan something, aka a cookie exchange, that people feel that it is ok to cancel at the last second! I mean some of us have been in the kitchen making cookies, making LOTS of cookies, to share and then BAM the email or phone call comes that says I am so sorry I won't be able to make it tonight for the exchange! I want to scream at 3 people so bad right now and I know the other lady coming tonight probably does too. It is now down to just the two of us which doesn't make for a great cookie exchange. Am I being unreasonable on this?