Writing fiction lets you be a little more emotional and unguarded, a little freer. Writing fictional characters is also really different from writing about real people. In nonfiction, you can only say so much about the people you interact with. After all, they're actual people, their version of their story trumps yours. In a novel, you can build a character, using certain parts or impressions of someone you know, and guessing or inventing others, without having to worry that your guesses or memories or inventions are wrong.