We can't control the winds or weather ahead- we can learn about the forecast, currents and tides, but the variables are too many to understand them completely-- you need to be ready to change the plan.
I was not born at sea, and spending many years of my life on land and on calmer rivers and ponds, a degree of intimidation exists whenever I cast off from shore. Your preparation and initial judgement only take you up to the decision point, and once you set off -- there are only two options: turning around and giving up, or pushing forward and succeeding.
The sea has challenged me, and built my strength in a way which no course or classroom could. While some focus on their strengths and continue on with their weaknesses, I prefer to squash my fears, using all my strengths to do so. The fundamental driver of success is determination and knowing you can do it. You won't do it right the first time, but you did it. Next time you'll do it better, building upon each experience-- adjusting your course.
So what are you afraid of? Yourself.