Many parents despair that they need to be more consistent in their dealings with their children. But sometimes this very consistency can be a problem.
Let's say you have just announced to your child, in a fit of frustration over some unpleasant conduct, that he will be grounded for the next six months and cannot leave the house for that time. Once your temper cools, you realize the lack of wisdom in this decision. However, in your desire to be "consistent" you are hesitant to change your mind. You don't wish to be seen by your child as a pushover.
Sticking with an unwise course of action doesn't teach your child that you are consistent; it teaches him that your are unreasonable. But you fear that changing your mind will send a message of weakness. However, if done well, it acutally communicates strength and confidence.
If you merely "cave" to your child in the face of their arguments, demands, or tantrums, then you are sending the wrong message. But if you let him know that you are changing your mind as a result of your considered reflection, you will gain, not lose, the respect of your child.
So you will say something like this: "Remember this morning when I said that you are grounded for six months? Well, I've been thinking about it, and I've reconsidered. That punishment is too harsh. I spoke before thinking because I was angry. I've decided instead that you will grounded for a week."
You didn't surrender to your child's entreaties or tirades. You showed him that your were a reasonable parent concerned more about making the right decision than simply being in charge. And by changing your mind, you gained rather than lost authority and respect in the eyes of your child.
So, if you make a sudden, impulsive, emotional, and misguided decision, don't hesitate to go back, acknowledge the mistake, and change your mind. That's not weakness, that's strength.