Promises

When does a promise mean something?
When You say I promise to do this, doesn't that mean that you will do it?
Isn't that a guarentee?
It's not to be broken right? Or is it just another word?
Me, I really hate it when someone say's "I promise". Because I don't know if they are serious or not. To me when you say "I promise" that is a binding contract. You don't forget that. You do everything in your power to fullfill that promise.
Otherwise why say it? You could just say yeah I'll get to it when I get to it. or yeah I'll do it. Thats easier to handle then someone saying yeah i'll do it I promise and then never do it.
Isn' that part of trust? And if someone keeps promising things and doesn't follow thru how do you trust them fully again?