Quotes (3) Promises

What is a "promise"? Why do people break promises? I think it's easy to say a promise, but it's hard to do it. Then why do you have to make a promise if you know within yourself that you can't do it? Basically, a lot of people does it. They promise things even if they know that they can't do it. But I also believe that there are some circumstances wherein you will have to really break a promise. But when? I also don't know. I just know that when a promise is broken, a "sorry" means nothing. :)) But what if the person that said sorry was really sincere? Hay~ Whatever. :))