It's been said to write out the first draft, and edit later. Let your first draft be crappy, and come back later when you're in "editor mode".
Some of us have been taught from an early age to edit as we go along, and that's typically what I do. Hallelujah for computers, where mistakes of "there", "their" and "they're" are gone with a few strikes of the backspace.
I read a book last night called "Writing And Personality: Finding Your Voice, Your Style, Your Way" by John DiTiberio which goes into Meyers-Briggs types of personalities (which every writer should be familiar with for their characters). I'm an ISFJ by the way. Also by the way, the book was interesting and is good for character descriptions.
It said that my personality type sits on things, and doesn't actually commit pen to paper after I have everything sorted out already. Normally I do that. A lot of times the stuff just flows, and it comes from who knows where - some font of wisdom that the muses spoon-feed me. I just write what the voices tell me.
Most of the time the stuff comes out fully-formed, like Athena from Zeus' head. (I had a pic of Athena and the muses on my blog for years because of that belief.) A lot of times, the first draft is the final draft. I write it once, then go through it looking for spelling or consistency errors, then I release it into the world. I read all my writing that I've done over the day before I log off for the night. Sometimes I'm surprised. Sometimes I'm disappointed. But I usually don't change it. It takes a glaring error (like the fact that something didn't exist at the time of writing) for me to change something that's already hit the blog or Protagonize. I either figure out my way around it or abandon it.
You notice that I abandon a lot, huh?
It's because I had an idea and getting to the idea was going to take me too long and be too boring for me to even write. Well, if it was going to be boring for me to write, imagine the person reading it! Maybe another way to work with the abandoned bits will come up. One never knows - but don't ever throw out the crap.