"Some people assume that authors write books because we have vivid imaginations and want to share our vision. Other people assume that authors must write because we are bursting with stories, and therefore must scribble those stories down in moments of propondidty.
Both groups are completely wrong. Authors write books for one, and only one, reason: because we like to torture people. 
Now actual torture in frowned upon in civilized society. Fortunately the authorial community has discovered in storytelling an even more powerful- and more fulfilling- means of causing agony in others. 
We write stories. 
And by doing so, we engage in a perfectly legal method of doing all sorts of terrible things to our readers. 
Take for instance, the word I used above, "Propondidty". There is no such word- I made it up. Why? Because it amused me to think of thousands of readers looking up a nonsense word in their dictionaries. 
Authors also create loving, friendly characters- then proceed to do terrible things to them. This makes the readers feel hurt and worried for the characters. The simple truth is that authors like making people squirm. If this weren't the case, all novels would be filled completely of cute bunnies having birthday parties... So now you know the reason why I would bother writing a book. Ask yourself this: would any decent, kindhearted individual become an author? Of course not." 
~Alcatraz Versus the Evil Librarians by Brandon Sanderson

By far my favorite quote...