I think a writer earns stamina by proving his or her ability to grow and develop. If all 7 Harry Potter novels had existed in a cartoony style, they wouldn't be the most popular children's novels of all time (I don't know if they really are, I just suspect so)! Instead, J.K. Rowling grew and developed, just as her readers were doing. We're all anxious to read whatever her next endeavor is, because she hasn't worn us out with the same ole' boring "stuff". The stories are consistent, loop holes all closed, language specific, though vibrant. William Shakespeare wouldn't be the world's most revered playwright if every story took place in Verona, starring fickle teenagers. Shakespeare grew and adapted to the audience's expectations, while still keeping his own integrity and style.