When you promise, keep it. Promise is an agreement from your soul, no matter what, you can’t break it.
Because you have promised, the person to whom you have promised has considered it will be kept and would plan further. If you break your promise you put other person in trouble and if he can’t meet those promises at his end the cycle carries on, it initiates a chain of broken promises.
Don’t give promise that you can’t keep. And if you have given, never break it. Personally, I never promise and when I do, I keep it.