The principle which is here at play is development.
The book, "The wizard of oz" offers a detailed analysis of the use of the hero's journey. It is the journey of Dorothy, from her home in Kansas to Oz and back again to Kansas, which passes various development stages.
Each friend Dorothy meets, they go on this journey to seek what they desire the most in life. After the long adventure, they come into contact with the Wizard in the Emerald City. The Wizard tells them that before he would grant their requests, they need to execute the Wicked Witch of the West.
Hence, the principle which is at play in the book is development.
To learn more about The wizard of oz here:
https://brainly.com/question/16994243
#SPJ4