I like to take the positive approach that maybe the fear arises out of the desire to be better at what we do. It's not as if others don't struggle with the same insecurity; at some point, I think most people harbor this type of self-doubt.
The cure? For me, it's to work harder. And always strive for the next level.
I think I read somewhere that it takes at least ten thousand hours to become an expert at whatever you do. That's a very long time, and speaks to the old adage that perseverance is every bit as important as talent. It's some consolation to believe that my best writing is still ahead of me, and I can't get there unless I just keep writing, writing and writing some more.
It seems my every Insecure Writers post always ends with: never never never give up! But it's true.
Hang in there, everyone. And visit the Ninja Captain Alex for links to the others in this great group. Thanks, Alex, for launching the Insecure Writers.