The Why Test
"No, we can't go to the park." "But why?" "Because I said so." That never worked, did it? It doesn't work on readers either. If our stories can't pass the Why Test, there is a motivation problem. The problem may be even deeper than why we allow something

"No, we can't go to the park."
"But why?"
"Because I said so."
That never worked, did it? It doesn't work on readers either.
If our stories can't pass the Why Test, there is a motivation problem. The problem may be even deeper than why we allow something to happen, or a character to act a certain way. Does the part/person in question have a justified existence?
Let's try it on my first draft of Fodder for Pigs.
I had to rip this information out of my head, and my readers probably would have done the same if they could reach me. Watch as it gets better in increments:
Why does the sheriff allow Mr. Campbell to torture people in his jail?
He's a coward.
Why?
He's scared of Campbell.
WHY?
Campbell claims to be from the militia.
He is the gosh dang law. So WHY is he afraid of the militia?
The sheriff has no deputies and is in a fairly remote place. The last time the sheriff refused to help out a militia member, he ended up with the whole lot of them. They ate all his chickens and butchered his hog, leaving him nothing for the winter. When he sent for help, he was told these monsters were the help. He feels he is a failure, has lost a lot of confidence, and his young family makes it difficult to stage resistance.
So get help from someplace else?
Campbell has convinced him the whole town (a mile away), is Campbell's eyes and ears and they would be "delighted to help". Not so.
Why does he exist?
Excuse my excessive thinking and over-writing for a minute.
He provides a setting for the story to begin. He has his own subplot. If it weren't for him, the two main characters would not survive for very long. He offers wise advice, but he is flawed. This flaw lends itself to Irony and Tragedy, but aren't I going for an Epic? Am I really?
You see, the "old man with the stick" must offer direction, whether good, flawed, or from a flawed person. He must show the protagonist the story's true/main struggle. Gandalf does this in Lord of the Rings. Atticus from To Kill a Mockingbird, Epic with Ironic overtones, also serves this purpose. A cowardly sheriff is hard to see in their lofty position, and yet he still completes the job. The sheriff's advice for David is to pull himself out of his stooper or risk losing himself entirely.
Hmmm isn't that advice he himself should follow?
But wait! There is another advice giver. The true "old man with a stick": The General. He has a cane that he uses fairly often over children's heads. He has mentored the protagonist in youth and shows up throughout. The General's advice was "blood don't wash out yo' shirt, it sho' as hell don't wash off yo' soul," as in don't stoop to that level, don't become the thing you hate. This is the advice that sticks in David's head, though unheeded half the time, and this is the defining moment at the beginning and end of the story. The choice he makes shows his development while sending half the readers into a fit and the other half into satisfied smiles.
The sheriff serves as a reminder, a replacement when there is no access to the "old man with the stick". The question persists though; after he serves his purpose, is his existence justified, or is he merely a plot device?
Why is the Why Test so hard?
I suspect we all have reasons for what our characters do or don't do. We have to dig deep to understand them. The reasons are stuck in our heads and need to make it to paper/computer. By putting them in the Why Test, we can usually identify their place in the story.
I like to think the sheriff is developed enough to be a part of the story. However, this should serve as a warning. Make sure your characters are not mere devices, but people.