I find that I do the same thing. I have a specific task to do, like finish a quilt, and I find all sorts of things that must be in order before I can get to the task at hand.
I think, at least for me, it is fear and uncertainty. I tackle the things I am confident in before starting something that makes me nervous. I guess to boost my confidence.
I call it the Ed Norton syndrome. Now I have revealed my age to you. FYI Ed Norton was Jackie Gleasons side kick in the old TV show the Honeymooners.
PS I am a Scorpio and a Rat!