In his essay "How to Write With Style," the incomparable Kurt Vonnegut dispenses the following advice:
Find a subject you care about and which in your heart feel others should care about. It is this genuine caring, and not your games with language, which will be the most compelling and seductive element in your style.
Although the essay trends more easily toward advice for nonfiction, this "genuine caring" lies at the center of all effective storytelling. And yes, it's important in the plot. Story is huge.
But it's even more integral to character.
Good fiction requires emotional investment. It demands empathy. It inspires loyalty.
But none of that happens without characters one can visualize in three dimensions. The vernacular in creative writing workshops focuses on round versus flat characters, and this is probably a useful way of talking about it. But to be more blunt:
Does anyone care?
If the answer is no, then the story's probably dead in the water. Jack Ketchum's Red succeeds because we see Av Ludlow in three dimensions. He's a sentimental man who has endured some terrible losses in his life and he wants justice. His simplicity, sincerity, morality and, for lack of a better term, his way so thoroughly endeared me to him that the "how" in his narrative predicament became less important than the "will."
I have to admit, I was worried that he wouldn't quite get his...well, I won't spoil it for you.
The same is true for Audrey Lucas in Sarah Langan's excellent novel Audrey's Door. Her tragic upbringing and attendant neuroses are so well rendered and so heartbreaking that we can't help but pull for her. Audrey's Door is a damned scary novel, but not as much for the bumps in the night as for the possibility that someone I've grown to care about as a reader might not be okay.
Characterization is king. I mean, if we don't care then what else is there?