on Jane Friedman site:

The best way to deepen and enrich our characters is to develop them from long before they enter the story we’re writing. Every character (really, every human being) struggles with one or more wounding experiences that create life-long emotional responses. These backstory wounds result in the lies our characters tell themselves, or what Lisa Cron in Story Genius refers to as “misbeliefs.”

By borrowing from acting techniques, especially those developed by Konstantin Stanislavski, writers can follow a logical sequence of development to create a character that feels real and alive while their wound and misbelief may remain buried and invisible—even to the character.