Brian,
It is indeed a mystery!
I think it is a question of inertia–we get so used to being one way with ourselves, our minds, our time, that it is hard to move into an altered state, which I believe writing is. Also, to write well, we have to give up control and allow the words to come through us without judgment, at least in starting the material and writing until there is enough down on the page to make good use of our editing and shaping skills. We don’t like to give up control, to be surprised by what we say, to try even at times to make sense of what the words are telling us. And sometimes they tell us things we have been trying to ignore.
But once we have moved beyond the inertia and our brain is in flow, we get such a high. Still, the next time we have to move once more beyond the fear of not knowing what we will have to say as well as the fear that our words are not up to the challenge of saying what we have to say.
Writing isn’t built in one session, though, and as writers we need to look for the words and phrases we put down that we want to continuing writing from and then continue, rather than get stuck in harshly judging our first drafts and freewrites as inadequate.
And guess where we learned such judging ways? In school, when we weren’t taught that writing is a process and where we had to write without sounding like we’d written what we wrote if teachers demanded “objectivity.”
Thanks for the question!
SB