It isn't based only on doubt and fear. Those happen to be predominant with writer's block, though. I might point out that ambiguity of scope may be summarized

It isn't based only on doubt and fear. Those happen to be predominant with writer's block, though. I might point out that ambiguity of scope may be summarized as doubt, and you do proceed to use fear as the third part of your list. But yes, procrastination in general is not only those things.