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.