Elizabeth Bear posted this, and I can relate.
I don't like the idea of writing a quota of words a day, or saying I have to write X words before I can stop, or saying "no revising until the draft is finished!" I don't like the idea that you Must Focus At All Times while writing.
Several things I've pretty consistently known about myself are that I need to finish things in advance of deadlines and that I can only focus for a limited amount of time. In high school, when it was term paper time, I'd be reading and making notes and going to the library for lit crit references, and getting my outline together (and because it was school and they were graded, I had detailed outlines), then I'd spend all day Saturday 2 weeks before it was due writing it out BY HAND (because this was the early 90s and we didn't have a computer) and revising it until I was ready to type it up. Then I'd read it, and I'd spend the next Saturday making sure it was right.
I think I was better at extended focus in high school than I am now, but I don't remember exactly what I did to crank out my term papers. It was a long time ago. Sometimes I hit a block, where the words need time to grow in my head, so I'll do something else, like read LJ or my google reader feed, but I recognize the importance of not letting myself get sucked into surfing the web or playing Flash games or Wikipedia diving, so I limit myself. Sometimes that's a sign that I'm done with writing for now/this session/today, and I take it as such and go do something else for a while.
But there are people who perpetuate the idea that in order to be a successful writer, you have to crank out X words per day or per session, and do Y or Z, which often includes No Distractions and to follow Procedure M to build your story. That doesn't work for everyone. You have to do what works for you.
And since Bear posted her missive, maybe I'll start to believe it, because hearing something and knowing something are different from believing something.