I used to be a perfectionist, harder on myself than I was one others, once called a 'self-defeatist' by a former bf. And I am trying to really think this one through, on how to give advice on letting go of the perfectionism, the type you describe. Because I am trying to pinpoint where that all changed within me. As odd as this may sound, I want to say it all just shifted in my head, around the time I was trying every technique in the book to potty train my oldest son. That all started a little over 8 years ago. And within 2 years time, it was similar to a paradigm shift in my view on life. Not one, tip, trick, book, word of advice(aside from they won't go to kindergarten in diapers) worked. And somehow, I absolved myself of holding myself up to anyone elses standards but my own. And the idea of 'perfection' flew out the window.