I have learned that people are going to do what they want to do.
They can make all the promises, assure you with "I'm gonna's", but they will never feel obligated to follow through unless they want to. I don't know why they feel the need to lie. Or perhaps they believe they will, or might...
Either way, I rely on nothing and no one. Even if someone swears they'll be there, I've already completely prepared for them to not show.