There isn't usually a single event or occurance that causes someone's self-confidence to bloom to the point of someone getting a business launched (that I've noticed).
But this is what most folks are constantly on the look out for. That "last" missing piece of information or whatever that suddenly fills their self-confidence guage to the point of actually going forward with their business plan.
Now that is not to say that single events can't cause someone to take the leap and become a real entrepreneur. I've come across a lot of people that have started businesses because of a job loss or layoff. Now I wouldn't call that a self-confidence boosting occurance would you? But I would bet job loss creates more entrepreneurs in business than any other single event.
Personally I think self-confidence is way over-rated when it comes to the tools one needs to start a business. I believe just plain old-fashioned courage is far more important.
What is business 'courage'? To me it's the ability to act when you are financially and professionally scared to pull out that credit card or take out a loan to start that business you've been dreaming of...but you go forward and do it anyway.