I just finished reading a play by Eugene O'Neill - The Iceman Cometh - which is , basically, the story of some people who hang out in a bar all day, everyday, get wasted and talk about what they'll do...tomorrow.
They're always just a few steps away from achieving their dreams. But they're pipe dreams, man , they'll never happen.
Your post kinda reminded me of that. I think we don't do a lot of things for fear of failure...what if we fuck up? So, to answer, nothing is stopping us, in theory.
But, to be honest, fear is what stops most of us, dead in our tracks.