Mickey Spillane famously said “They read to get to the end. If it’s a letdown, they won’t buy anymore. The first page sells that book. The last page sells your next book.”
I can see the creative writing students rolling their eyes. Mickey Spillane wasn’t exactly a great prose stylist. But the guy knew how to write books that sell. He sold 225 million of them.
And he sure was right about that last page.
He didn’t mean you should leave characters hanging off cliffs so the reader will be forced to read the next book. Cliffhangers make readers feel betrayed. If somebody reads a whole novel and doesn’t find out what happens to the characters, they get angry. And angry readers don’t buy more of your books.