Fictional vs. Dramatic Characterization
There is a difference between fiction characterization and dramatic characterization. While the fiction author has the latitude to just inform the reader in prose, the dramatic author must have the characters unfold before the audience. The audience learns what the character is like just as they would if they met them in real life. This is, in my opinion, the true key between writers of fiction and drama.
I found it difficult to develop the characters using only their words to inform the audience as to the nature of their principles. I think that any writer of fiction can learn by writing a few one-act plays. It would help them to use the characters instead of just telling the readers some fact about the characters.
For an example, in A Streetcar Named Desire, Stella is a minor part in the grand drama between Stanley and Blanche, but the audience can pick up many of her characteristics by her words and actions. She idolized Blanche, and she still loved her sister, as seen by Stella breaking down when they hauled Blanche off to the asylum. We can also see that she loves Stanley, even though he hits her and delves a bit into mental abuse. The audience can set up Stella as someone we can all feel sorry for.