How screenwriting is different from writing novels

I made a lot of mistakes in writing my first novel, but an inadvertent one had to do with the story's abrupt ending.

Now, unlike mistakes caused by carelessness (editing) or inexperience (the original book cover), this mistake was the result of being too experienced in a different genre---screenwriting.
In screenwriting, a writer has about 120 pages, or 120 minutes to tell their story.  This means that everything has to be distilled to its essence, and screenwriters strive to capture only...