Three. Perfectionism, honestly stated

You have probably been told that procrastination is perfectionism. It is a satisfying explanation and the evidence is thinner than the confidence with which it gets said.

What does seem to matter is a particular flavour of it. Not having high standards, which plenty of people have without this problem. It is the worrying kind, the fear of the work being judged and found wanting, which makes contemplating the task unpleasant, which is the mechanism from lesson two.

So treat perfectionism as one contributor among several rather than as the explanation. If it is yours, you will recognise it. If it is not, do not go looking for it, because the actual driver is often much duller: the task is boring, or you genuinely do not know where to start.