Chekhov was the first dramatist to realize that, on stage and in life, what is not said explicitly is often the decisive dramatic ingredient. In The Cherry Orchard, Lopahkin fails to declare his love for Vanya by getting himself tied up in a redundant conversation about lost galoshes.
But it was the job of the German Expressionist playwrights to remind us that people often do not listen to each other at all, and that in real life there can be a complete absence of dialogue, leaving us with mere monologues running along side by side.
To watch characters talking to each other when they are not communicating at all can be an unbearable experience. For us as an audience it quickly becomes apparent that all opportunities of establishing a relationship, or of solving a problem are being tragically missed.
Brecht and the other Modernist dramatists were determined to stage what they saw as contemporary reality. They understood that a photographic reproduction of the external lives of individuals could do no justice to the complexity of the social, economic and political factors which determined modern existence. In the West civilization was now over-organized and individuals had to relate to their own experience and to each other in highly structured societies.
These dramatists wanted their actors to step outside of their roles and to show the audience if they approved or disapproved of the characters they were embodying. They wanted to bring an end to the pretence of the theatre as the real world seen through a missing fourth wall.
They wanted the stage to be treated as a stage.