The Argument For Normalization

"The goal of normalization in simple terms is just this: to store each fact in exactly one place. When you put each fact in only one place, you always know where to go to read it or write it. When facts are repeated in the database, the application programmer has an increased burden to make sure they are all consistent."

http://database-programmer.blogspot.com/2008/10/argument-for-normalization.html