Your characters live and breathe, just not quite the same way we do. They are just as real in the way they react and the way they work through problems. One of the things we as writers must do is to get to know our characters in any project. KNOW why they do what they do. KNOW why they open door B instead of A. A character thrown in to a story without the author knowing their purpose and their quirks will understand why the “red shirt” guy in Star Trek is an ongoing gag to this day.