Is it important for a writer to know the entire story before they start working on the book?
I know people will disagree with me, but I think the answer is-yes.
This doesn't mean the story can't change. As the characters develop and come to life they may alter what takes place, however, I believe if you have the action mapped out and you know the key points you want to hit you are more likely to finish the piece.
Here is why.
It is very unlikely a book will be finished in one sitting, (maybe impossible). It's easy to pick up where you left off if you know what happens next.
Knowing the story helps strengthen the character development. When you know what someone is going to do, it makes you think about how they will act.
Stories may change as they are written, but having a rough draft in your mind can help guide the process.