Think about the last time you organized your room.  You probably put all of your toys in one spot,  the books on a shelf and your clothes in your dresser.  You did this so you the next time you go to find something, you will know exactly where it is.  

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Well, authors do the same thing.  They organize their writing.  In this way, when the reader is looking for specific information, it will be easy to find since it is grouped together.