From Dave Farland:
I once got a letter from a reader who asked about heroes and villains that switch roles in a book. The author pointed out that at one time I mentioned that in most cases we don’t get too deep into the mind of a villain. As authors, we avoid penetration in villains.
There are a couple of reasons for this. First, it can be disturbing and distasteful. I have a brother who has worked as a detective, and on a couple of occasions he had talked to me about interviews that he has done with child molesters. I can tell you with great certainty that I wouldn’t want to spend any time at all in the head of one of them, and if your audience is subjected to a revolting character for too long, they will set the book aside.
The second reason to avoid deep penetration in a villain is that it can undercut the surprise in your story. For example, let’s say that we have a villain who devises a complex plan to, say, murder an enemy king. If you as an author get deep into the villain’s head, if you reveal too many details of that plan, you can take the element of surprise out of the story.
Please note, though, that this can also work for the story. It can get the reader to wondering, “Gosh, how is the hero going to get out of this one?” So you can basically give up some surprise in order to raise the level of suspense. So often in storytelling, we must sacrifice one effect in order to gain another.
. . . .
First, pay close attention to your characters’ motivations. Your hero can win the hearts of the readers early, and so long as his actions are understandable, the reader will follow him down a dark road for quite a long way. So you have to keep that deep point of view in your hero. Now, with your villain, you might start out with him using only shallow penetration, but then move into deep penetration as you go. Show why the villain is doing what he does. Ask yourself, does he have any misguided ideals? Was he trained to be this way? Does he act out of any noble desires? Does he feel trapped into behaving as he does?
Second, with both your hero and your villains, let them apologize for their deeds. Give them good reasons for doing evil. For example, when I was a prison guard, in at least a couple of instances I saw other guards manufacture evidence in crimes in order to try to convict the inmates that they most suspected. The good guys tried to use deceit to fight crime. Meanwhile, I’ve known villains who used the law in order to gain their own ends. My own grandfather, who worked for the FBI during prohibition, hid behind his badge as he arrested smugglers on the Canadian border, and then sold the stolen goods.
Link to the rest at David Farland