Recently, I was in the Alberta foothills and saw my first blue bird. I was about four feet away from it when I took this photo. The bird had no fear of me or the other people around. We had invaded its territory, but it didn't seem to mind. It stayed on the branch long enough for me to go to the vehicle, get my camera, return, and take a few photos. Shortly after I took this shot, I stepped a foot closer and the bird flew away. It knew its limits.
Like the blue bird, I try to write without fear of invasion, but with a strong sense of what I need to defend. Sometimes this defence is against my own zany ideas. However, I try as much as possible to only attack these in the editing stage, not when I'm first getting the words down, because I never know when some unexpected thought will improve the story or trigger a different one.
I sometimes write scenes that I really like, but on a second look realize that they aren't part of the story. I put these aside. These might end up as part of another story or poem, or just an interesting idea. Often they are an unnecessary tangent or just don't make sense with the flow of the story.
Other times, I write something new which doesn't go with my original idea. Once it has simmered a bit, I realize that it is important to the story so change the landscape of the story. Sometimes the addition of this new idea is a lot of work, but it improves the story, poem, or article.
Just because something wasn't in my original plan doesn't mean it can't be part of my writing. At the same time, just because I wrote something or thought of something doesn't mean it has to remain in my story. The more comfortable I am with the territory of my writing and the essence of what I am trying to write, the better I am able to identify what improves the work and what detracts.
Invasion can come from other people as well. Like the blue bird, keep in mind the integrity of your piece and remember that you are the gatekeeper and not everyone is correct. Anytime you ask someone for feedback on your writing or you get unsolicited feedback, remember that you are the author. It is your work, and you know the territory. However, sometimes since you know what you meant to write, you might have missed a step or two.
Don't be afraid of critique, but also don't take everything everyone says at face value. The problem they see might really be an indication of a problem somewhere else. Or it is possible that they are wrong. However, for the most part when someone says something is missing or confusing in my writing I find that there is a grain of truth in it, even if it isn't in the place they point out.