This is second to my first footnote. There is a fundamental difference between fear and doubt. Fear is, in most cases, good for you, because it forces to you to decide one of two things:
Fight or flight.
For you to decide on one, you'd have to conduct an analysis of the situation and apply the best of your knowledge (or brawn) to evaluate the odds, that is always good.
Doubt, on the other hand is all in the mind.
Never, doubt anything, anyone and yourself. Doubt, in my humble opinion, is purely imagination. You assess the possibility of failure without actually knowing what has to be done.
That's like fortune telling, and we all know that is not an exact science (similar to economics, :-)
My philosophy is simple:
If you find yourself in doubt, it means you have lived the catastrophic end that you have imagined, so you might well do what ever it is you are 'doubting' to do.
It's like that movie (forgot the name), when an America guy is in Japan and he is framed (photographed) for 'attempted' rape, but he actually did not do anything and he says:
If I'm going to be punished for a crime I did not commit, I might as well commit.
Obviously this analogy is extreme, but you get the jist.
Although, every time I doubt myself, it re-affirms the fact that I believe I can do it, but just too chicken to do it.
I have been 'in doubt' for quite sometime, now.