Joss Whedon's Character Writing Advice

Everyone knows Joss Whedon, right? He's a writer, producer, director, script doctor, and executive producer to name a few of the hats he wears.  He is an amazingly talented man.  Some of his writing credits include Buffy the Vampire Slayer, Toy Story, Firefly, Titan A.E., Alien Resurrection, Angel, and The Avengers.  Can you imagine the things going on in this man's head?  Does he ever sleep with that kind of imagination?  And while I know none of those things I listed are novel writing, he gave some advice that I've really been thinking about as I write my new novel.

He said:

"Everybody has a perspective. Everybody in your scene, including the thug flanking your bad guy, has a reason. They have their own voice, their own identity, their own history. If anyone speaks in such a way that they’re just setting up the next person’s lines, then you don’t get dialogue: you get soundbites. Not everybody has to be funny; not everybody has to be cute; not everybody has to be delightful, and not everybody has to speak, but if you don’t know who everybody is and why they’re there, why they’re feeling what they’re feeling and why they’re doing what they’re doing, then you’re in trouble."

I have a minor character in Pocket Full of Posies that has really been clamoring to be more of a major character and I've been fleshing him out.  This "thug flanking my bad guy" has a history and an identity and even though he started out non-speaking, he's now becoming an integral part of my book.  And as I was doing that, I read what Mr. Whedon said and it resonated with me.  I started looking at my other non-speaking people.  What's their story?  Why are they there and what's their reason?

Doing that has helped me to know my story better.  I didn't think I could know it any better than I did, but it added a whole other dimension to it.  I can tell you the reason for a lot of actions now, where previously it was just setting up the next character arc.  It's been a great exercise for me and advice I will definitely use in my future novels.

What do you think?  Is it valuable for you to know the whys and wherefores for each character both minor, major, and the ones who are firmly in the background?