This short final chapter of the idea stage has to do with a writer's instincts. The instincts are something you have to learn to follow as you write. It's that niggling feeling at the back of your mind that your story took a wrong turn. It's that tired sensation you get when you need a break. It's that raging burst of inspiration that motivates you to write five thousand words in a day.
Your instincts are paramount when writing. We'll discuss how to deal with writer's block later on, but know for now that many cases of writer's block happen because you ignored your writer's instincts. You can plan as much as you want, but if you don't listen to your brain when it tells you something needs to be changed, your story will fall flat on its face. And if you don't listen to your mind when you know it needs a break, you won't be able to squeeze a single word onto the page.
There's also a time to ignore your instincts: mainly, when writing a rough draft. I recommend not doing any sort of mechanical editing when writing the first draft, because if you get caught up in small details, you may not be able to finish it. The key to a lot of early stage writing is to just write. Don't listen to the voice in your head that tells you the draft is bad; you know that, and you'll fix it later. But you can't edit a blank page.
However, there is a time and place to backtrack when writing. If there's a large wrong turn that could alter your entire story negatively, or you feel like you're getting blocked, fix the problem. The goal of drafting is to get a blueprint onto the page so when you rewrite, you have more sense of direction. If you can't find the problem, get a friend to read over your work. Having a fresh set of eyes is extremely valuable in the writing world.