Honesty.

Everyone has flaws. Promises to 'be good' are bound to be broken, often unwittingly, often carelessly, not because we're 'bad' but because we're human. I don't promise to 'be good' but I promise to be honest for whilst uncaring deeds can be forgiven, dishonesty eats through the ties that hold a relationship or a friendship together. Honesty is as important to a person as breathing. Building credibility takes years but is lost in a fraction of time with few uttered words.