There's a famous scene in the movie "Goodfellas" where Joe Pesci's (Tommy) character tells a funny story in a restaurant for his fellow mobsters, and Ray Liotta's character (Henry) maniacally laughs at the story with mischievous delight. At the conclusion of the story, Henry tells Tommy that he's a "funny guy," and Tommy immediately takes offense- 'Funny how? Like a clown? Do I amuse you?"
The scene is a famous one, an Oscar clip actually, that helped Pesci win an Academy Award for his Goodfellas role. Now when watching this scene materialize on screen, it is so iconic, and so revealing about the characters that one imagines Pesci's standing in a casting room, before a team of casting directors reading sides off of a page while reciting the "funny how?" dialogue.
But it may surprise you to learn that the scene wasn't actually written in the script, or even conceived in a casting room during an audition. The scene was actually constructed during 2 weeks of rehearsal that the actors were allowed to experience before filming of the movie commenced.
It was during this rehearsal process where the actors began the find the character's voice, and started to play with the backstory for the roles they were playing. Pesci improved the story, which was actually based on a real-life story that he experienced, and well. the rest is history.
This story illustrates one very important thing about creativity: It doesn't always happen in a writer's room, or in a casting room. Sometimes, it needs to flourish during rehearsals and run-throughs.
So if you're a filmmaker or a casting director that is creating a shooting schedule for your actors, be sure to prioritize the importance of rehearsals within your creative process.