J. K. Rowling has had an interesting career before she penned Harry Potter. She has been a teacher as well as worked at Amnesty International.
It seems to me she drifted from one thing to another untill she found the courage/conviction to sit and pen down Harry Potter.
J K Rowling says that she always knew that she wanted to write stories. She knew her "Harry Potter" (my use of "Harry Potter" is in a sense to imply that which is your deepest desire and your life's calling- work that you were meant to do)
What if you don't know what your "Harry Potter" is?