Most of the time, my "editor brain" is turned on. Okay, always. I look at everything with a critical eye, constantly asking myself, "How can I make this better?" I do that with my own work, with my clients' work, and (sometimes not for the better) with my friends' and family's work. It is a difficult thing to turn off.
But the "writer brain" is drowned out by the "editor brain." When the "editor brain" is turned on, the "writer brain" withers and dies. This is because the "writer brain" feeds off of creativity and freedom. When I am focused on editing--on sheering and pruning, on improving and polishing--there is no room for wild, messy, sloppy creative freedom. My "editor brain" sees my creative idea and immediately starts fixing it, which tells my creative "writer brain" that the idea was not perfect... which of course it isn't, not right off the bat. But my "writer brain" is sensitive (as creative types tend to be) and it immediately shuts down and sulks, refusing to get anything else done.
It is a difficult balance to try to have a "writer brain" and an "editor brain," and that is why it is always helpful to have another person's "editor brain" look at your own creative work. Because it allows your "writer brain" to remain creative, excited, and enthusiastic, without having to worry about all of that boring, tedious, and oh-so-necessary revision.
So, as it turns out, even editors need editors when there is writing to be done.