I saw a bumper sticker that admonished "Don't Believe Everything You Think." I had been trying to put this notion into words myself for a while when I discovered this pithy advice on the back of the car ahead of me. I find it hard to put into practice. We generally take what's in our heads as true.
If you don't question yourself you'll have what the world rightly considers disorganized, magical, or delusional thinking, or not really thinking at all. Thinking is like believing, but sieved through observation, trial, questioning, and doubt.
Artists, open to intuition, to imaginative reaching and risk-taking, are especially susceptible to self-delusion and denial. Dreams aren't really open to correction.
But I believe that powerful and enduring art results from the interchange of conviction and doubt, a process of urging something into existence and then questioning its validity. Doubt and uncertainty, with accompanying self-questioning, discomfort, and setbacks, feel unproductive, yet only by passing through this state will anything ultimately worthwhile emerge. Doubt on its own doesn't get you anywhere. Conviction, the belief in what you do, gives art its authenticity and motive power; doubt, its durability and integrity.