You can try and try – you can make allowances for contingencies and mix-ups, but there are still going to be errors. And when errors happen, forget a promise, meeting, or commitment; then someone is going to be hurt, upset, mad, or disappointed.
Rather than becoming upset, defensive, or guilty, maintain your bearings and remain compassionate. You should understand that there’s simply nothing you can do – other than your best. You didn’t intend for it to happen, you did everything you knew how to prevent it, yet it happened.
In fact, most of us will do everything within our power not to, yet it’s still going to happen. And it will happen again. It’s time to let it go and focus on doing the best you can.