Why keep a journal?

Have you ever realized that most people forget the smallest details of life? Think about the time when you started high school.  Did anything interesting happen? Was it just an ordinary day? But when you think about something major, for example 9/11, how do people remember where they were, what they were doing, and how they found out? Little details are seldom remembered on a normal day, but when something major happened, a person can remember what exactly went on. This is one secret of the brain that we do not understand yet.
What if there was some way we could remember an ordinary day? I only know of one way.  That is writing.  I admit, I write in a journal to try to remember those ordinary days and details in full effect.  Not many people now keep a documentation of their writings, but some do, and those are the ones that are one day famous for writing or have an autobiography published by the time they are forty.  Think about Anne Frank, who kept a journal during her time of WWII, and is now dead, but very widely known throughout the world for her life story. There are also many writers that remember their experiences because their life was so traumatic, like Jeannette Walls in The Glass Castle, and Into Thin Air by Jon Krakauer. 
All of these people went through traumatic events, and both ended up being successful writers due to just telling their own story.  Laura Ingalls Wilder, wrote many books based on her life experience, even though there was no trauma, but just a story that she probably documented.  I can think of so many books that were based off of true stories: Caddie Woodlawn, Shadow of the Titanic, To Kill a Mockingbird, Marley and Me, and  Into the Wild.  These stories were taken from true memories and had a fictional book play around them.
Many movies based off of true stories include: Secretariat,  Dolphin Tale, Soul Surfer, Hidalgo, Seabiscuit, and The Blind Side. These stories often are based off of a miracle, but there really does not have to be a miracle to make a good book or story. That's why I recommend everyone write in a journal.  Your story might be amazing too.