Or rather, it should be hard. It seems like a lot of people are under the impression that writing is "making up whatever crap you want and putting it down on paper". Sure, maybe this is how many writers get started, but I would offer that good writers, who write something that sticks with you long after you read it, work really hard.
If you're a good science fiction writer, you might actually research some science (gasp). If you're a good fantasy writer, you might learn about mythology and mysticism. The level of work should reflect what your readers get out of it.
I've read stories that were obviously made up on the spot, and although some of them were good, none of them left me with a profound sense of...anything, really. Let's consider Stranger in a Strange Land by Robert Heinlein. It's funny, I actually just read a review of this book that really slammed it, but I suppose that reviewer was an idiot. What can you do?
The book in question was written back in the 60s and took the author about ten year to write. Part of this had to do with the political climate and some of the ideas that the book offered (not that they're all that racy these days). But that's what I think a good book should offer: ideas. Not necessarily rhetoric or religious in instruction (looking at you C S Lewis) but an idea or a feeling that resonates with its audience. Is my writing there yet? Since I'm being so judgy and all? I don't really know. I hope that one day it will be.
