To a certain extent, your characters need you to let them live, the way a parent has to let her child be himself. In other words, you have to think of them as real people. Once they become real in your head, they start acting on their own, which often becomes a problem for you, when they don't want to do what you want them to do.
There's a famous story about this. When Margaret Mitchell started Gone With the Wind, she was aware of the ways characters can mess up a writer's plans by acting on their own. She knew she wanted the novel to end with Brett telling Scarlett, "Frankly, my dear, I don't give a damn!" and she didn't want to give the characters a way to screw it up (by reconciling, or finding another love, for example), so she wrote the last chapter first, then the penultimate* chapter, then the preceding chapter, etc., until she'd written the whole book backwards.
I don't know if the story is true, but it's a beaut...
*my second-favorite $.75 word, after "defenestrate."
Hmm... I just noticed something. Typewriters all had a "cent" sign, a "C" with a vertical line through it. My 'puter keyboard only has a dollar sign. Wonder when they'll finally stop minting pennies?