To Promise or Not To Promise?

I think that promising someone something is not a good idea. I imagine I am Aurelius. I kept the magician a promise to pay him a thousand pounds but in the end, I only got five hundred pounds. If the magician do not want to let me go I will be killed by his wand. That means, if you promise someone something but before you paid him back some thing happened, you must still pay him back no matter what. In Canterbury Tales, Aurelies(which is me) lost everything in the end, his beloved. so promising is not really good.