Ray Bradbury
"Love. Fall in love and stay in love. Write only what you love, and love what you write. The key word is love. You have to get up in the morning and write something you love, something to live for."

Books written:

From the Dust
Farenheight 451
An Illustrated Life

J.R.R. Tolkien
"I cordially dislike allegory in all its manifestations, and always have done since I grew old and wary enough to detect its presence."

Books written:

The Lord of the Rings series
The Father of Christmas Letters

J.K. Rowling
"It does not do to dwell on dreams and forget to live."

Books Written:

Harry Potter series
A political fairy story