Are you familiar with Robert McKee’s STORY? It’s a rich and valuable text on writing techniques. Although it’s slanted for screenwriters, its principles work equally well for authors of prose.
As McKee explains it, making a character complex involves establishing conflict on two or three levels in any given confrontation.
There’s external conflict, internal conflict, and relationship conflict. Any scene can be written that deals only with external conflict or only with relationship conflict, but it won’t be complex unless they’re combined or internal conflict joins the mix.
External conflict: Daughter versus Mom over the girl’s choice of college. Mom wants Daughter to attend State and be a teacher. Daughter wants to attend Prestigious U and be anything but a teacher.
Internal conflict: Daughter doesn’t want to be a teacher like her mother, yet she knows it’s a practical, fairly secure career path. In Daughter’s heart, safe equals boring. In Daughter’s mind, safe means she might finally escape Mom’s criticism. Daughter really wants to be a writer, which isn’t practical or safe. Also, Daughter isn’t sure whether she has the talent to achieve her dream. Her passion for the written word is at war with her desire to please Mom and to have an independent future.
Relationship conflict: Mom has raised her children as a single parent on one modest income. She can’t afford to send Daughter to the expensive university. She feels that Daughter tends to be impractical and foolish. She wishes Daughter would listen to her advice and benefit from her experience. She’s afraid that Daughter is too much like Ex-husband, a dreamer with a fancy degree that never achieved anything notable, except to break her heart.
Now, consider how the scene will go if it’s written only on the level of external conflict. Then compare that with how its conflict will rage if all three levels are utilized. See the difference?