This fear creeps in when you want something new, that you have never done before, where you don't have yet experience, you don't consider yourself an expert, and you keep postponing the action because you only want to start doing it when you are good enough at it or when everything seems perfect. The high level of expertise that you want to reach before you go out is often self-imposed and works as a block on the road to your destination, making it hard to even get started. But it's ok to be bad at something you've never done before, that is the whole point of doing something new in the 1st place!