As I finished reading another Harlequin romance a few nights ago, one that was, in my opinion, successful, I caught myself wondering about what made it so.
That's when I realized (or maybe remembered) that it reminded me of writing essays in college and university. Why? Because that's what it is: an argument put forth by the writer. Like an essay, if the story is convincing enough, I'll agree with the argument and maybe even take it to heart.
A Harlequin romance is perhaps the simplest example: the author presents us with two characters, puts them in situations that cause them to fall in love, presents the counter-arguments of why they could not possibly be together, and then proves to us why they should be. When done well, the story satisfies, and I walk away happy.
And it's true in any story: a convincing argument keeps me reading. I want credible characters. I need a plot strong enough to hold me in the argument's sway, and a setting vivid enough to make me imagine it as if it were real.
In fantasy, this is taken one step further: the author not only has to present a powerful story, but a believable world. Even when the plot is set on Earth, the magic must make sense.
The goal is to sell your argument.