When Back to the Future hit theaters on July 3, 1985, it brought to fruition a project that had been more than five years in the making.

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The concept began with writer and producer Bob Gale, following a visit to his parents’ home in St. Louis. While looking at his father’s old high school yearbook, Gale began to imagine what it might have been like if they were classmates together. “Would I have been friends with him?” Gale pondered out loud in the Making of Back to the Future documentary featurette. “Or would I have hated his guts?”

Upon returning to his home in California, Gale described his idea to friend and frequent collaborator Robert Zemeckis, who loved the concept. So set in motion the process to bring Back to the Future to the big screen.

The story centered on Marty McFly, a teenager accidentally sent back in time when an experiment alongside his friend Emmett “Doc” Brown goes wrong. Once in 1955, Marty accidentally encounters his future parents, setting in course a series of events that threatens his own existence. Marty has to get the two to fall in love, while also avoiding terrorizing bully Biff Tannen and trying to find a way to get back to the future.

The film became a passion project for both Zemeckis and Gale, who continued pushing forward despite many obstacles. For years, the movie was turned down by studios that deemed it unlikely to be a hit. “We were getting the same exact message from everybody: ‘This is just not for us,’” Gale recalled, noting that most studios were looking for raunchy comedies like Porky’s at the time.

Watch the 'Back to the Future' Trailer

Steven Spielberg would eventually sign on as producer, giving the project some major clout. Still, the filmmakers initially had to settle for their second choice of actor in the role of Marty McFly, after Michael J. Fox was originally deemed unavailable.

Though the story would eventually go on to resonate with generations of fans, the script was a constant source of concern during the movie's production, as changes were continually being made right up to - and even during - filming. As noted by the website Hollywood and Spine, many scenes were changed or completely cut from the film. These included the opening introduction of Marty and Doc, Marty's lavish escape from high school detention and George McFly being locked in the bathroom during the Under the Sea dance.

Upon its release, Back to the Future became a blockbuster hit, making $389 million worldwide. The original film’s success launched a franchise that would go on to include three movies, an animated series, video games, comic books, theme-park rides and even a stage musical.

Still, the classic film would never have become an iconic hit were it not for several smart - and in some cases lucky - decisions. Here are 10 ways Back to the Future could have been very different.