A play is never finished until it's mounted. Though written by one, it's produced by dozens and perceived by thousands. Novels, short stories, poems, essays and reviews once published do not change. Plays in production change continually. Every time the play is done these components alter.
Theatre is probably the oldest entertainment form of humankind.
Probably because it always tells the story, and there's always human conflict. As Pulitzer Prize winner Marcia Norman points out, a play must deal with one central character who wants something and by the end of the play must get it or not. We witness in The Ice Wolf what makes Anatou beg the Wood God to transform her into a wolf. We witness what prompts Lizzie in Sunday Gold to sacrifice her gold nugget and help Annie escape. We witness in Angel in the Night why Pawlina is ready to die rather than admit the truth to the interrogating Nazi.