Let's face it: we all make dumb mistakes. Dumb as in the mistakes, not necessarily the person making those mistakes. Because despite how intelligent the person is, he or she can still make mistakes that simply don't make sense. The number one reason is allowing emotions to control our actions. However, our conduct is truly the only matter we can control. So we must take task seriously and with caution. When we do, success is almost inevitable with awareness and practice. If you happen to have made a dumb mistake, move on as quickly as possible. Salvage a bad mistake with a positive response. Nobody who has ever succeeded would fault someone making an honest mistake. Apologize, don't make excuses, and focus on the present. Do not be discouraged. Doubt exacerbates a mistake. Chin up, make the next step a step forward.
Keeping promises is hard. It requires us to do things we don't want to do. But keep those promises you must do. Otherwise, do not make them in the first place. But since you have made them, you must keep them, especially if it would benefit all those involved including yourself.