“A promise must never be broken.”

This quote implies that you should never break a promise because you will not be trusted with things that you used to be trusted with. If you decide that you want  to break a promise then you will not be granted trust. This can affect you in a lot of way they won't even trust you with everyday things. Promises were not meant to be broken. it s the complete opposite promises were made to kept true to. You always have to keep your promises because it's you that it makes look bad. And shows that you have no commitment.