This link has a short clip of Francis Chan explaining why he is leaving Cornerstone.
Now I know he doesn't have a for sure spelled out reason for why he is leaving but he knows God is tugging at his heart and he is moving where God is calling him. He is stepping out of the boat, he is putting full faith in God and not letting the fears get in the way. I would like to say I wish I could do this, but lately I feel like my calling is going to be shot down. So is it really a calling? Am I hearing wrong, or might others hear wrong? This is the difficult thing with God. I just hope that when I have it all figured out I will follow God wherever he sends me just like this worthy example set by Francis.