it is said that when writing a script we must take into account the end, and this is true, because if we do not have clear where our characters are going at the end of the road, probably the film will fall in the last scene.

This is very true. Even in writing plain stories. I see people saying they write as the spirit leads them without actually picturing the ending.

Actually, this is the little flaw in free writing. Sometimes that method works out good, but most time it doesn't. And the aim of every story writer should be to ensure the reader is satisfied all the way from the top to the bottom. If not, he'd be losing the reading audience.