A brief edition, 7 years later, as this article is still receiving attention.
AS a webcomic artist who has now produced over 1,000 pages of work with no hesitation, I should amend this article with the following summary:
Art-block is caused by a lack of creative purpose. Purpose is the best means by which a vacillating artist might finally become motivated again. Whether it's as simple as the need to capture a beautiful image, like a sunset with a loved one, or as dire as the need to communicate an imperative revelation before death, this purpose is the key to allowing the feeling of importance, which will allow artists to undertake as great a task as making art.
Avoid irrelevant information.
Understand your own desires.
Feel no shame.
We all get art-blocked at one point. "I don't want to draw" or "I don't feel like drawing this..."
By understanding what art-block is, we can take steps to avoid it in the future, and pos