Well, I've found myself in the not-so-fun position of looking at some very significant secondary characters rather blankly and thinking: 'Okay, so WHAT are you doing?' and 'WHY would you be doing that?' I know their histories rather fully. I've written their dialogue and it comes across naturally enough with each sounding different from the other. I know their names, their likes and dislikes, their loves and hates, and some of their driving goals.
But I've realised something ... I know them the way a person knows their boss or a friend and it's just not close enough. There's knowledge there but no real intimacy. There's a certain spark of recognition that's missing. While the protagonist does his thing I don't really know what everyone else is doing. How do they exist outside of the protagonist? Who are they really? What are their plots?
I'm wondering how I could best determine this. Perhaps do a blow-by-blow of what others are doing when off-stage? Perhaps do a mind-map and brainstorm all the aspects of the characters and what that would likely drive them to do? Perhaps brow-beat them into submission by writing character interviews and demanding they reveal all?
I'm just not sure.
What do you do?