When, if ever, is it right to break a promise or a date or appointment? Why?

To answer this question I first think we need to decide why people make promises. Promises are made every day and some of them life changing, take marriage for example. When two people get married they agree to spend the rest of their lives together, 'till death do us part'. This is a promise, therefore a showing of love? You would say yes maybe if you look at it that way. But what about corporate promises, to write a signed 'promise' that I will give you half of company if you pay for it. Is that then a promise or a compromise? Perhaps promises are made as a sign of love and compromises are made to survive. Now I will go back to the question 'When, if ever, is it right to break a promise or a date or appointment? Why?' Let's look at our wedding scenario again, how does the bride or groom know that he will love his spouse in 50 years time? He makes the promise on a matter of faith, faith in himself. But the groom used to love listening to the 'Sex Pistols' but now he thinks they are the most terrible band in the world. Okay, that excepted your now going to say that 'well yes, he did love them, but he never promised to love them forever'. But again this time around the important thing is faith but is it that truthful, can it predict the future? That's what it is doing, his faith is saying 'I know that in 50 years time I will still be in love', maybe faith is the greatest psychic? If it is then how come it got so many other marriage 'promises' wrong, how come it didn't predict those truthfully? Therefore I have come to the conclusion that promises shouldn't be made, unless your psychic of course!