I am that kind of person that can spend a whole day in a coffe shop, reading and writing with a coffe. I've always loved reading, but the recent two years I realized I love to write. I write when I feel like it, and often while listening to music because it gives me a certain feeling to write about. 
Writing fanfiction is a way to write about a world someone else has already made. Maybe that's why I love it so much.
Of course, writing on your own is lovely as well, because as always in writing, the limits don't exist.