How Much of Confidence is Overconfidence?

Every time someone sure to win fails, others attribute a reason, almost instantaneously - "he was overconfident".
But, how much of confidence is overconfidence?
Usain Bolt was sure he would be the Olympic Champion even before the 9.69s run began. And how would have people reacted if he failed in winning the race, after showing the 'V' sign even before the "Go" word? Of course, news channels would have been beaming with special bulletins that criticized the act of him imagining himself to be a winner as one of brimming overconfidence. 'Sports specialists' would start advising their listeners as to why one should never celebrate success before achieving it.
But, visualising success and enjoying the fruit before it flowers are all techniques that stand out among self-help techniques. These have been used by many with considerable success in their endeavors. And these are one of the sure fire techniques that allow human bodies to activate the mechanisms that are required in order to achieve the feat that is to follow.

Still, when you are confident, and when you lose, people criticize you. These fangs are inescapable. You can't shake off the agony that grips you either.

So, how do we make sure that we are not overconfident and that we have just that critical amount of fire burning to take us through?
If we are able to answer this question, we will be able to save ourselves from that embarrassing moment when our confidence present itself as overconfidence to others.

If you decide not to practice,
If you decide not to be worried about it,
If you decide not to look forward to it,
If you decide not to prepare the failure speech,
Then, my friend, you can make sure, you are overconfident.

But, otherwise, every gesture of confidence that you make are completely justified, and the people who call you 'too confident' are the people who deserve sympathy for commenting about what they don't know.

Be confident. Be overconfident. (Because, as for anything else, sky is the limit for confidence)