Reminds me of the rule of Michael Kevin Powell that when you are 60% ready, go for it. The other 40% is your ability to think on your feet and resilience to the opposition and frustrations that will invariably pop up.
The Simple Dollar » The 40/30/30 Rule: "What is the 40-30-30 rule? Simply put, it’s an argument that when you prepare for anything in life, only 40% of the preparation is physical – the rest is mental. Thirty percent of preparation is technical skill and experience, and the second thirty percent is the willingness to take risks."