For most of recorded history, acting was, simply put, a performative act. The theater was a place of grandiosity, where actors used a demonstrative, often histrionic style to convey their character's journey. 

But that all changed with Konstantin Stanislavski. As Travis Lee Ratcliff illustrates in a new video essay, the Russian director revolutionized the craft of acting at the turn of the 20th century. Perfecting his method by trial and error in experimental theaters in Moscow, Stanislavski developed a system predicated on the art of experiencing. He encouraged his actors to have emotionally truthful reactions and experiences, revealing complex shades of vulnerability in a quieter, more ruminative manner. Thus, realism was born.

In the 1950s, American theater schools adopted and further developed Stanislavski's methods. The result can be seen in the emergence of actors such as James Dean, Marlon Brando, and Montgomery Clift, all of whom internalized Stanislavski's psychological realism in their performances. 

Today, we take realism for granted onscreen. But were it not for Stanislavski, the Oscar for Best Actor or Actress might go to a performance that is more decorative than emotionally truthful.