About Back to the Future Day
In "Back to the Future Part II," Michael J. Fox's character goes to October 21, 2015.
The date was chosen for one simple reason: It was a day, theoretically, the Chicago Cubs could win the World Series.
In the movie, Marty McFly notices while time traveling that the Cubs finally win the world series in 2015, and buys a sports almanac so his younger self can make bets and get rich when he returns from the future. But his nemesis, Biff, gets his hands on the almanac and gets rich instead.