A few years ago I read Anne Lamott's Bird by Bird, which is even better than people say. I was reminded of this quotation via Oliver Burkeman's Help! How to Become Slightly Happier and Get a Bit More Done.

Perfectionism is the voice of the oppressor, the enemy of the people. It will keep you cramped and insane your whole life... perfectionism is based on the obsessive belief that if you run carefully enough, hitting each stepping stone just right, you won't have to die. The truth is that you will die anyway and that a lot of people who aren't even looking at their feet are going to do a whole lot better than you.

Anne Lamott, Bird by Bird