I have more of a problem getting characters to do what I want them or need them to do. Very specific example - right now I'm working on the final lost chapter of The Butterfly Legacy. I need, somehow, for Lois to move from feeling emotion A to the opposite end of the spectrum where she feels emotion B. And without pages and pages of introspection or forced dialogue, I don't know how to get her there. Top that off with a Clark who keeps coming out a tad bit too defensive and I'm thoroughly stuck!
Mostly, though, when I write, I know where I eventually want to be. The characters often do take me on detours which result in scenes I'd never imagined or, more likely, with new characters that I'd never intended to expand upon. Adam from Rage is a prime example - he was a throwaway who ended up becoming a major player in helping Clark work through his issues. Totally unexpected.
I love it when you have a kernel of an idea and the characters just jump on the wagon with you. I also think letting the characters jump in makes for more in-character portrayals as well as adds interest to the story - turns you never expected to take are often the most interesting ones.
Lynn
