From the Twelve Virtues of Rationality:

The ninth virtue is perfectionism. The more errors you correct in yourself, the more you notice. As your mind becomes more silent, you hear more noise. When you notice an error in yourself, this signals your readiness to seek advancement to the next level. If you tolerate the error rather than correcting it, you will not advance to the next level and you will not gain the skill to notice new errors. In every art, if you do not seek perfection you will halt before taking your first steps. If perfection is impossible that is no excuse for not trying. Hold yourself to the highest standard you can imagine, and look for one still higher. Do not be content with the answer that is almost right; seek one that is exactly right.

Perfectionism considered harmful

Jennifer Kromberg writes, on the hallmarks of a perfectionist belief system, that:

Things are either black or white- no vaguely defined area of in between or close enough. Things in your life are either right or wrong, good or bad success or failure.

Such a belief system, she argues, interferes, among other things, with forming intimate relationships, causes anxiety and a sense of shame, and leads to ones self evaluation being judged on external achievements rather than who you are.