I am scared to quit my job and start a business, what should I do?

I have a secure (but unsatisfying) job working for the government. I have a business idea that I think would be successful, and I've done my research and have written a solid business plan. Just recently, I've come across two other parties that are interested in starting the same business in the same location. I'm stuck and scared. Should I proceed with my business idea or should I stay with my secure (but unsatisfying) job?