Because we are afraid that it might not work. Because we are afraid that the world is going to find out things we are not proud of. Because we are afraid that we don't have what it takes to do art. Because reassurance releases us from responsibility to choose for ourselves.
And what if the project didn't work? What if we chicken out of the hard decision and chose the path that we won't rather talk about? What if instead of the tyranny of "you told me it was OK", we had to face the consequences of the change that our art created in people?
Just as we can't learn to do 1000 push-ups in one day without being comfortable with suffering, we can't create art without experiencing the fear.
The only reassurance artists need to know is that they beat their inner dragons just today. Until the next time.