What is promise about?

Promise is just a written or spoken declaration that one will do or not to do something. Promise is come out from heart sincerity but not just to play a fool with someone or just to If someone can't fullfill his/her promise, why he/she still promise someone? I kept wonder something. Not only marriage is a promise but friendship, relationship between family, business or matter in life are deal with promises.. But how many people will really fulfill their promise? Promise is really a unique matter. It maybe bring happiness but also will cause disappointment to others at the same time. Since that incident happened, i don't believe in promises anymore. Because i learned that "Don't try so hard, the best things come when you least expect them to." When out of expectation, everything is just a surprise for you! Our life will be happier as well. Ganbatte! ;)