People backing out of things last minute.
My girl scout troop is going to an event this weekend. We had 3 parents sign up with their daughters and an additional 3 girls sign up without parents. It's been less than a month since we signed up, so not exactly forgettable.
Now I'm taking 5 girls by myself, and had to spend time trying to get the whole car pool thing worked out.
I wish I could say this was unusual, but it seems like every planned event is like this.