The easiest thing that can make you fear for the worst outcome. You can be scared of the smallest task on the planet yet your fingers might be trembling while doing it.
According to me, it is because we are not sure that things might go the way they usually go because life has got tremendous amount of sarcasm and wants to have a joke at you at times.
What I say is, do it. Howsoever scared, feared you are. Just do it if you see a single positive spark in yourself and if it makes you feel satisfied.
(a little messed up thoughts right now)