I am an inveterate perfectionist, though my perfectionism takes a unique and insidious form (below). Distinguishing perfectionism from the desire for excellent results -- the former a compulsion, the latter an admirable drive essential to doing pretty much anything -- is difficult.
How do you tell them apart? I think it depends which end you're looking at. I know there were many days when, as a teacher, I left a class all pleased with myself because I had delivered, was brilliant, informed, articulate, insightful, sensitive, etc. It hardly mattered if no student was able to do anything with what I taught them. It's a little like the classical scientific definition of work -- apply all the force all you want, but if the object doesn't move, you haven't done any work.
Perfectionism sees things only from the front end; the perfectionist worries entirely about what he or she is doing, not how it moves others. It's a compulsive effort to feel better because you satisfied some self-imposed precondition. There's a kind of hermetic imperviousness to the perfectionist that is ultimately self-referential, ineffective, and incomplete. Reminds me of that heat-sealed plastic blister packs everything comes in -- the object arrives perfectly intact, but you have to destroy it (and hurt yourself) to get it out.
(My own form of perfectionism is compulsive efficiency. I make a lot of mistakes that way. Not the good kind, the dumb kind, the unnecessary kind. It's actually remarkably inefficient, because I have to go back and do things over. I honestly don't know what the hurry is).
Photo credit: commons.wikimedia.org, Photo by Tktktk