Nuff said. Criticism, fear of failure, fear of rejection by your peers.
Uck. And it gets really weird when you are a professional and have to create in collaboration with a team. I always try to be in the sandbox. You know how an 8 year old plays in the sandbox? Lost in thought? Creating a world? All in his head and just there doing?
Or like how a great athlete finds that zone? It's like meditating. That's where I try to be and when I'm not I'm practicing.