Theater of Cruelty means a theater difficult and cruel for myself first of all. And, on the level of performance, it is not the cruelty we can exercise upon each other by hacking at each other's bodies, carving up our personal anatomies, or, like Assyrian emperors, sending parcels of human ears, noses, or neatly detached nostrils through the mail, but the much more terrible and necessary cruelty which things can exercise against us. We are not free. And the sky can still fall on our heads. And the theater has been created to teach us that first of all.

Ch. 1 - The Theatre and Its Double (1938, translated 1958)