Jeff Pulver asked this question on his blog yesterday. A number of people, myself included, told their stories. Fascinating reading.
clipped from pulverblog.pulver.com

Today’s Question of the Day: If you are an Entrepreneur, How did YOU become one?

If you are or ever have been an Entrepreneur, what event in your life pushed you to go out on your own? What is YOUR story? Is this something that “just happened?” Or was this planned? Would you recommend the Entrepreneur lifestyle to others?
  blog it