You don't have to keep the ending, but write the last five pages, and it will feed you. Always write the dialogue first. Description is worthless. The camera does that. Only through dialogue do you know the scene's intention.
Dialogue is everything.
It doesn't have to be theatrical. It's important because it makes you think about motive. Writing cinematically means you don't give a shit about motive. Dialogue is people structuring people. For me, dialogue is paramount.