Characters have dramatic functions, but the reader or audience needs to identify with them as real people as well.  A necessary but difficult task is to intertwine the personal and structural aspects of each character so that they blend seamlessly together and become interdependent in a unified person.

If your character is a protagonist, for example, what personal qualities or previous experiences have led them to become a protagonist, the Prime Mover in the effort to achieve the goal?  Similary, if your character is wishy-washy, how does that affect their ability to function as a protagonist?

By integrating both the structural and personal elements in every character, each will seem to be driven by real motivations, enacted in a truly human manner.