In an article on the innovation tools website (here), Stephen Shapiro talks about the fact that while it's good to have goals, at some point it becomes counterproductive to focus on them. Here's part of what he says:
"Although goals and performance targets are useful tools, they can also have a detrimental impact on results. When people are future fixated, their creativity and overall performance diminish."
He gives an example: "the true story of a high school student who became increasingly anxious over passing her upcoming final exam in math, always her weakest subject. She studied incredibly hard, all the time focusing on her goal to pass her exam. In spite of her efforts, she failed. She pleaded with her teachers to give her one more chance. They did. This time, instead of concentrating on the goal, she used a powerful creativity technique. Her first conscious thought each day when she awoke was to visualize herself as Condoleezza Rice, the U.S. Secretary of State, a very successful, highly educated woman. Dr. Rice wouldn’t worry about a high school math exam, right? By imagining she was someone else, she stopped agonizing and gained more confidence daily. By focusing on the present rather than the result, she scored a 93%, her greatest performance with less effort."
In terms of writing, if we get too hung up on what will happen to a manuscript or script when we've finished it, that takes our attention away from the moment. In that moment, our obsession should be how to make it the best piece of writing we possibly can.