Have you ever been thinking bout roleplaying games and think do I need all these books?
Then you think "Do I really need all these tables?" And "Do I really need all these dice?"
One day I thought about all of the above and decided to create a game for myself without anything other than my minds eye aka the good old imagination, and a pencil and paper.
After doing so for a time, I ended up with enough characters and storyline that I was able to create a book.
Here is a link to that book.