"What I have to know about a story is only a fraction of what I can tell about a story."
An author has to know how their world works. Otherwise something odd is going to happen and readers will call 'foul'. At that point they'll either dismiss the story or Fan Wank. This is especially important for Fantasy and Science Fiction writers, who will (at some point) have to explain the mechanics and limitations of their magic or science or risk losing them to 'plot device' status. This means doing a lot of thinking and a lot of self-research.
When I started the second chapter of "A Mage's Power" I realized I didn't know how the new world I created was supposed to work. At the time I didn't even know its name. So I took a break from writing. It must have been two months or more. I thought about how magic works, where monsters come from and the kind of society that would develop along side such a threat. I thought about the structure of the nation that Eric stumbles into: politics, geography, culture, economics, etc. Any detail of Eric's life: the food he ate, the clothing he wore, his paycheck, etc I had to pin down in order to create the world he lived in. The most pressing question, of course, was: how would a real society handle a boy from another world that was dropped in their backyard by a trickster god that will appear if you say his name three times?
The answer to these questions can be found here at the free preview of "A Mage's Power".
That quote is from me, by the way. I said it during a summer class titled "Topics in Creative Writing: Jack Kirby's New Gods". Yes, comic book legend Kirby. It involved how he used the comic book medium to tell stories and juxtaposed it with illuminated manuscripts and poetry written by William Blake.