The simple reason 'Back To The Future's' screenwriter chose October 21, 2015 to be the day Marty McFly would travel in time

October 21, 2015 is “Back to the Future Day.”

It’s the day Marty McFly and Doc Brown travel to the future in their time machine, the DeLorean, in Stephen Spielberg’s “Back To The Future: Part II.”

The date was carefully 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 travelling 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.

“The Cubs winning the World Series was the most absurd thing we could think of [for someone to bet on],” the movie’s producer and screenwriter Bob Gale tells The Wall Street Journal’s Mike Ayers.

“If the Cubs were going to win the World Series, what date would that be on? In 1988, when we wrote this, there was only one set of playoffs, not two. If the World Series was going on and the Cubs were going to sweep the World Series, it could’ve happened on October 21. That’s how we arrived on that day.”

In 1988, the Cubs went 77-85. In 2015, they have gone 97 — 65.

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