If you made a promise to someone, you should do all that you can to keep it. There was a time when a man’s word was his bond and for him not to live up to his word a cause for social ostracism and personal shame. This doesn’t mean that there may not be just reason to explain to someone that due to unforeseen circumstances your personal ability to meet your obligation has deteriorated to the point that you need to renegotiate the terms of the promise, but to deliberately ignore your obligation to that person is indeed morally problematic.
