Most of the time when I hear someone say they can't do something, it's not that they are physically unable to do it, but that they don't want to do it or are afraid to do it. Take my niece for example, she "can't" drive on the interstate. She knows how to drive a car, she has her own car, she lives in a city with miles of interstate snaking through it so there's plenty of opportunity for her to practice, there's no reason in the world she "can't" drive on the interstate by herself. But, she won't, she's afraid to do it.
Do you know how you get rid of the fear of doing something that you should be able to do? You go out and do it. Start small and build up. If you're afraid of heights, start by standing on a step stool and looking down. When you're comfortable with that, stand on a chair. And so on.
Granted there are somethings that one should be afraid of like rattlesnakes and alligators. Those are healthy fears. Those are keep you alive fears. Those are good ones to have and to keep. It's the ones that are messing up your life, that I am talking about.
So how does this apply to writing and publishing? If you're afraid of writing crap, then sit down and write crap. If you're afraid of letting people read your work, share it with someone you trust. If you're afraid of rejection, submit a short story that you aren't as emotionally attached to as your major WIP. Whatever that fear is that is keeping you from realizing your dreams, conquer it by doing it.
*Climbing down off my soapbox*