Thirty years ago, the blockbuster release for the July 4th weekend was a film about a young man trying to rescue his parents’ marriage. Yes, Back to the Future involves time travel, special effects, and some dizzyingly creative science-fiction plotting, but the story at its core is a simple one, and its stakes are appreciably low. Just as Jaws ignited a box-office revolution ten years previously as a tale of three men in a boat after one shark, Back to the Future was a genre-defining hit in 1985, spending 11 weeks at number one and spawning two sequels—all without resorting to over-budgeted theatrics.

Strip away the time-travel facade and Back to the Future is a fun, zany small-town comedy, with its nastiest villain a high school bully and its biggest triumph a kiss between his two victims. Director Robert Zemeckis seized upon the concept of Marty McFly’s DeLorean trip to 1955 while looking through his parents’ basement and stumbling upon relics from their graduating class. He pitched the idea to Steven Spielberg, who agreed to produce the project. The strength of the movie is that its most fantastical element is rendered as something any audience member could imagine: the bizarre and frightening experience of meeting your parents as their teenaged selves. Compared to the current era of summer movies, so focused on omnipotent superheroes doing battle on a planetary scale, that simplicity feels revolutionary.

It also serves to disguise Back to the Future’s more absurd plot details. The movie’s hero, Marty (Michael J. Fox) is a teenager refreshingly free of angst. He’s in a band, he has a cool girlfriend, and his best friend is the middle-aged scientist Doc (Christopher Lloyd), who lives on the outskirts of town and has stolen some plutonium from a group of Libyan terrorists. It says everything about the breeziness of the script (from Zemeckis and Bob Gale) that these revelations (Marty and Doc’s May-December friendship, the shocking and violent appearance of the Libyans) have an air of plausibility.

In another actor’s hands, Marty’s friendship with Doc might come off as a symptom of extreme teenage disaffection, but Fox’s nice-guy charm smoothes things over without much fuss. Zemeckis notoriously filmed weeks of footage with a different lead, Eric Stoltz, who gave the role a much darker, method acting-infused spin, before firing and replacing him with Fox, his original first choice. The then-23-year-old was best known as a sitcom star in NBC’s Family Ties, and with those multi-camera acting chops came the ‘50s vibe Zemeckis wanted. When Marty picks up a guitar and plays a Chuck Berry riff perfectly, it just makes sense—he feels cut from the cloth of that era of post-war American exceptionalism where anything was possible.

The similarities in scope between Back to the Future and Jaws aren’t coincidental—Spielberg directed Jaws and played a major role shepherding Zemeckis’ vision to the screen. Back to the Future was a salve for the darker, edgier, early ‘80s era in Hollywood—Spielberg had misfired with the excessively gory Indiana Jones and the Temple of Doom in 1984, a year that also featured gritty R-rated box office hits like The Terminator and Beverly Hills Cop. In 1985, the top box office films were flag-waving tales of American glory like Rambo: First Blood Part II and Rocky IV, along with heartwarming throwback films like Cocoon and The Goonies. But Back to the Future topped them all, literally traveling back in time to tap into America’s small-town ‘50s nostalgia.

Once Marty arrives in the past, all he really needs to do is ensure that his parents (played by Crispin Glover and Lea Thompson) get married, perhaps with a little help from the band at their high school dance, while avoiding the evil antics of local bully Biff (Tom Wilson). Yes, Marty might just end up inventing rock and roll as a result (the phone call to Chuck Berry is such a hilariously false note it’s hard not to laugh) but that’s just one of Zemeckis and Gale’s clever little details. Time-travel fiction is notoriously hard to write without getting overly buried in complexity: Back to the Future remains the gold standard for keeping its logic in check throughout Marty’s trip to 1955 and back.

This July 4th weekend, another time-travel franchise is getting rebooted for the umpeenth time. Terminator Genisys dips deep into temporal vagaries to justify a film that recasts all of its leads except for Arnold Schwarzenegger, while still explaining how he’s aged 31 years since the original entry it’s aping. It’s utter nonsense, and worse than that, it spends too much time tying itself in narrative knots trying to explain its existence to have anything left over for its characters. Time travel is a worrying element for any sci-fi franchise a studio might want to hungrily reboot, and Back to the Future feels especially vulnerable—the DeLorean is sitting right there, after all.

Fear not. Robert Zemeckis promises such a reboot will literally happen over his dead body, saying, “We’ve seen a lot of sequels that are made years and years later and I don’t think I can name one that’s any good.” It’s a lesson Hollywood still needs to learn, and Back to the Future teaches it well. Forget established brands or CGI-laden setpieces. Invest in your characters, keep the stakes realistic, and have your happy ending feel hard-earned—even if it’s as insignificant as a kiss at the school dance and a successful drive home.