The ending, I mean.
For me, this is the absolute critical part of a script that makes or breaks the production. I can't say how many times I've been carried along by a story only to feel betrayed at the ending by some unexpected, illogical, near-magical contrivance.
A story is a series of events that follow each other logically (even if individual human choices seem to be anything but the case). Choices lead to a conclusion. The journey could end in success or failure. But it must satisfy. It must be logical. It must be inevitable.
Yet, false endings abound. We are surrounded by them.
“You can't send them home depressed!”
“That's such a downer. No one will go see that.”
“Nope. Must be upbeat. That's what people want.”
Which happens more if the story is a comedy. Comedies are supposed to end upbeat, and oftentimes we can allow a certain amount of...massaging... to arrive at a happy ending. (Unless they are dark comedies, in which case we're left at the end with a character getting out of one fix and smack into another. We're not supposed to laugh at this, are we? But we do. We smirk and shake our heads because the ending we're left with is an honest one. And in many cases, oh yeah, we sympathize. That could have been us.)
But for more serious efforts, doctored (crowbarred) endings conjure up a last-minute inexplicable (a) turn of events, or (b) change of heart, or (c) piece of evidence, saving our hapless, near-doomed protagonist from ultimate disaster. Because you can't get the audience all involved and then disappoint them, can you? Because box office totals will plummet.
The ancient Greeks used a dramatic gimmick called Deus Ex Machina (God from Machine), in which, at the apparently ultimate failure of the protagonist, a crane lowered (or a trap door raised) an actor playing a god who then, goddily destroyed the antagonist, changing the impending disaster into a happy ending. In our Disney-esque times, when a last-minute insipid plot device arrives to !!Save The Day!!, I call it a Deus Ex Rectum. And I feel cheated.
Audiences remember endings. They know if they have been massaged, smoothed out, or abruptly changed at the last minute in order to avoid audience disappointment. The audience may go home whistling, but they will recognize the subterfuge and know that, despite the happy tune, the story they have invested in has been manipulated. They well know life does not always end with a party and a song.
An honest ending appears, to the human sub-brain, as if no other ending was possible, that all the choices made during the telling led to this final moment. An honest ending works. Be it happy or sad, honest climaxes build bonds between the author and their audiences. The audience believes that the author will treat them with respect and give them the truth, and that raises the dramatic bar far, far above the insidious feel-good pap forever smothering the mainstream.