Promises

Why do we make promises? 
We make promises with people to give them confidence in you, that you will do what they have asked.When someone promises you something, you expect them to fulfill it. When you promise someone something, you should do so with the intent to follow through with it.
So why don't people keep promises?
I don't know exactly why...  It's different for everyone. When I make a promise to do something I do my best to fulfill it. Now, granted, sometimes the promise you made is harder to keep than you thought, and you can't kep it. But at least you made the effort. You put in all the work or effort you could, but something was stopping you. But what about the easy promises. You promise someone that you will help them.. you promise them that you will be kind to them.... you promise to do something, like accompany them to something they are nervous about.  you promise to comfort them when they need you, you promise to be there for them....  why are these so hard to keep?
Selfish people need a selfish answer...  Unselfish people need no answer, because they would kep the promise they made you. 
I sometimes wonder why people get your hopes up for something when they don't intent to follow through.  when you make a promise to someone, they count on you.  so do what you say.