Go here to be inspired with a list of 16 questions you should ask yourself if you're starting a new project, setting out on your own, etc. I'll add my own...What happens (to you, the market, etc. ) if you decide not to do it?
Does someone else replace you? Do you a leave a void in the lives of prospective customers? How does the world not change? In other words, what's the consequence of not doing it?