It’s the uncertainty on how things will turn out .
Be it on the thought of trying do something out of regular. Starting something, taking the first initiative, venturing into something unknown.
Or when you don’t know how to handle something. Since you don’t know what & how of the things , you are scared. The fear is there as you either don’t have the solution to that something or you are not sure of the solution .
The key to all this is finding the solution. No matter whatever is the issue there would be some way out. The difference would be on how easy or tough that path is & how practical it is to the situation .
So keep looking for solution which will help manage things bringing in uncertainty .