David Mamet offers strong advice in this pared down clip from movie commentaries, such as this:

It’s hard to write a drama — because it’s hard to write a drama with a plot, because a plot means that you have to at the end of the drama resolve that problem which gave rise to the drama in such a way that it’s both surprising and inevitable as per Aristotle. The thing is, can you turn the film around in the last 10 seconds — one of the hardest things in the world to do.