If our deepest fear is to be "powerful beyond measure," (as Marianne Williamson asserts), the obvious question is, Why would anyone fear their own power? Don't we all want to be powerful and great?
No, because once we recognize that we have the potential to be a potent force in the Universe, we also realize that any attempt at achieving something magnificent means
we could fail. And, because failure is perceived by most as sucking, we avoid activities that might cause disappointment, embarrassment, frustration and/or pain.
if we succeed, people will be jealous and not like us, and we like to be liked.
there will be expectation pressure. Great people are supposed to be great all the time.
it will take a ton of effort to A. become great and B. maintain greatness. Thus, there are people with extraordinary potential who consciously choose not to put in the work required to reach it.
Still, the trouble with 1 through 4 above is that when we choose not to go after greatness, it's not just ourselves we're letting down. It's the rest of the Universe, too.