When you write a book, your goal is to write a first sentence that will force a reader to read the first chapter, and then to write a first chapter that will force a reader to buy the book. If you are very good you will then deliver a book that will have the reader folding down page corners to mark particularly good sentences and passages and remember your name. And go back to the book store with their credit card, of course.
Want to see this in action? Go buy Catherine Ryan Hyde's Electric God immediately. It's that good.