Creating story is a process. However long it takes to complete your story—weeks, months, years—be prepared for requests for changes.
An editor may suggest rewriting an entire section.
A producer may cut scenes.
An agent may ask for more tension in the middle.
A producer may cut a character or ask that he change personality.
An agent may ask for a stronger or different ending.
A publisher will more than likely change your title.
A professional writer makes these changes—without complaint. Getting a story to the final destination, whether produced for the screen or published in the book world, will require changes. One of the touchstones the industry sees as the sign of a professional is your ability to make the changes.
If you have a strong desire to keep a section you need to present your rationale and sound defense delivered without emotional fanfare for keeping a part of your story. If you want your story published or your screenplay produced, don’t get stuck there.
When you get that notice of acceptance, that phone call from the agent, be prepared to work on changes. It is part of the process.