Nervous is perhaps the wrong word, but I certainly have a healthy respect for mother nature and am aware of the risks of my profession. Having lost colleagues in the past (helicopters), I have realised that there is only so much one can do and the rest is up to God, or circumstance for the non religious.
Managing the bit that I can control is hard enough work, and often involves gut feeling. When I start to feel "unhappy" it is time to review all options available, including not flying that particular trip.
I would think that anyone who is truly fearless becomes a danger to himself and those around him.