"Perfectionism" is probably related to Conscientiousness from the Big Five. Perhaps it's also related to Neuroticism. My hypothesis is that Conscientiousness causes you to have a high bar for your performance, and Neuroticism causes you anxiety when you aren't meeting that high bar.

Going along with Neuroticism, perfectionism may also be related to self-esteem or a need for agency in a particular area. For instance, during my insanely perfectionistic days, I would try to solve any word or logic problem that I ever came across, even if it wasn't a good use of my time and energy. I think the motivation was that I needed to prove something to myself.

Update: Wikipedia's article on Perfectionism) concurs that it may be related to Conscientiousness and Neuroticism.

This suggests that the main ways to deal with perfectionism are:

• a) lower your bar for success (e.g. don't set it higher than the task actually demands, or higher than is practical given your allotted time for the task): "OK, this is good enough... time to stop..."

and

• (b) better cope with your anxiety when you fail to reach whatever bar you are measuring yourself by: "I'd like to put a bit more work into this, but no sense in beating myself up..."

I've used both strategies successfully in my own life.