I think you're going to have to tell us a little bit more about yourself if you want us to give you acurate advice. It comes from your childhood, you say, but what happened, more specifically?
Based on the little information you gave, all I can tell you is to realize there is nothing wrong with making mistakes. Being fully aware of that makes one able to try out and fail and try again and fail and try again without feeling any embarrassment or shame or any negative feeling whatsoever. That's really important because the more you allow yourself to make mistakes, the more you make mistakes. The more you make mistakes, the more you learn from them. The more you learn, the better you become and the better you become, the more you trust in your own abilities (〓self-confidence).
Now, in case we're talking about a task that you absolutely shouldn't fail (like something that concerns your work), just going into it head first probably isn't the best thing to do, but you can always test your abilities by trying something that resembles the important task. For example, if you know you're soon going to have to debate in public, but your confidence into your ability to defend yourself with correct arguments is so low you're scared you'll lose, try to debate with people online first. It's anonymous and if you lose, you'll have learned that your standpoint was wrong and gained new insights into the debated subject. If you win, you'll have gained more confidence into your ability to be right and to defend yourself with logical arguments. In both cases, there are only major gains and no major losses.
So go out there and just live your life without caring too much!
With that being said, have a nice day. :)