"A promise must never be broken." by Alexander Hamilton

This quote means that if you make a promise you should never break it. Only good promises should never be broken. This is because a promise is the most important thing to keep. As in if a promise is broken bad consequences can happen. Just keep in mind that if you  don't want anyone to break a promise you shouldn't break a promise. For example being a good person and making right decisions is a promise to yourself that you shouldn't break.