Wading in Slowly

I thought I was ready to do this. I have managed to sign up for a site, but I haven't submitted anything yet. I keep starting an article then feeling like it isn't good enough to submit. Is this common? I am fighting the feeling that I'm getting in over my head. There is so much I don't know and I am so afraid of failing that I can't seem to make myself try. If I don't post for  a few days you'll know that I'm just sitting here staring at a blank word document and trying to psych myself up to write something. I am not going to post until I actually have something submitted!