As a script consultant and producer, I don't think there's a steadfast rule, as each writer may find a different source of initial inspiration and it's important to honor your own unique process. In my experiences in working with screenwriters for over 15 years, I have found that once an idea begins to form, log lines can be helpful with respect to bringing focus and direction to your story -- so that it becomes a reference point from which action, character and plot may flow. Log lines therefore, are not only sales tools for pitching; they also can create the spine to your screenplay during the creative process. If you can define your core concept by encapsulating it into a sentence or two, this reference point can be an effective springboard.
At the same time, it's not good to be slavishly wed to one particular way of doing things so you can allow for your muse and the unexpected to come into play. Many times the surprises, the elements you didn't plan, become the moments that make your script stand out. You might even find once you've started your screenplay that you will need to go back and revise your log line. But the purpose of having one to begin with served its purpose in getting you to this point.
I hope the above is helpful. Please check out my website www.la4hire.com as I specialize in assisting writers elevate the quality of their writing and execute their vision.
Wendy Kram, Producer/Owner
WK Productions & L.A. FOR HIRE CONSULTING
firstname.lastname@example.org * www.la4hire.com
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