What do you do if you realise that you've made a wrong decision?

This such a very hard question, i think :), in my case Once I decide something then will take action right away. If decisions don’t bring the results I want, I will learn from it, correct it right away and move on.
Most things take trial and error to create the outcome you want. No one gets it right all the time. And this is not a bad thing. Who do we think we are, Masters of the Universe?

I think you should clarify your question, at which point did you make that wrong decision? For instance, in terms of human resource management, that might be: you chose the wrong person for a position in your company? You promoted the wrong one?

Anyway, whether what it is, and whether the wrong decision that you've made has brought a consequence to an individual or the whole company, or how big it is, I do not think it's a big problem, as a matter of fact. Because wrong decisions make progresses. We seem to learn better, get more valuable lessons and keep it in mind longer from failures or times when we make wrong decisions. Make it your business to look at how you can correct the mistaken decision so that next time when you have to face such a problem again, you already had experiences at least. You never know how to deal with something until you encounter it. Learn from the past and make it right this time, never fail for the same thing twice. That way, you will end up realizing that it's time to let it go instead of keeping negative thoughts.

Successors consider wrong decisions as the chance to gain lessons of experience.

First is to consider the impact - will it hurt someone - meaning personally or physically? If the answer is yes then the first thing to do is make a correction and make it quickly. You need to maintain your integrity above all else regardless of the consequences on your self.

In business there are political situations that you need to be aware of. Sometimes it is a sign of strength to readily admit the bad decision and "fall on your sword" letting everyone know it was a bad decision. That is ok as it shows your integrity and determination to do want is right even if you started off on the wrong approach. There are other times however when there is no need fall on your sword and if you did it would just weaken you and possibly the new solution you have..We could probably write a book on that.

What is most important though is to define your "recovery". That is how do you recover from a bad decision to minimize the error and maximize the impact of the right decision. You could make a bad decision about your own financial affairs. You would identify the problem and your options, then go into a "recovery phase". If it affects a personal relationship it is the same thing. You need to identify the issue and determine what you can do to recover from the bad decision.

Always remember that the best managers make mistakes and that the magic of a great manager is in the recovery. We all think of Steve Jobs as Apples leader but seem to forget he was their CEO and left because he was not ready to run a company that size and then returned many years later.

A helpful book is "Crucial Confrontations: Tools for Resolving broken promises, violated expectations, and bad behavior" and also "Crucial Conversations: Tools for Talking When Stakes Are High".

Good luck

You should always try to correct a wrong decision as the consequences can be to great.