Even among fan theories, there are clichés, and perhaps the most common fan theory is the classic, "It's all in their head." Well, according to Redditor /u/atomicbolt, this premise may actually explain a lot about the hit 1978 musical Grease.
This theory is plausible in the case of the classic film because so much of what happens both in front of the camera and behind the scenes of Grease is straight-up bonkers. Characters abruptly change personalities, cars fly, and high school students break out into choreographed song and dance.
Grease is the story of the high school love affair between Danny Zuko (John Travolta) and Sandra Dee (Olivia Newton John). Pretty much all of the Grease characters are memorable: car-obsessed hot-rodders, beauty school dropouts, and Frankie Avalon. They sing and dance their way through a loving pastiche of '50s teen musical tropes; however, every story has a dark side. It turns out Grease may be far darker than anyone ever suspected - with the possible exception of Redditor /u/atomicbolt.
The movie opens with gentle, serene shots of a beach. Danny and Sandra are on summer vacation and have fallen in love. They kiss on the beach, and then the film cuts to funky, animated credits. The next time we see Danny, he's back at school, bragging to his friends about the girl he hooked up with in the song "Summer Nights." In the song, Danny sings he "saved her life - she nearly drowned."
According to Redditor /u/atomicbolt, "Sandy actually did [perish] on the beach that day. As she [went under], her brain deprived of oxygen, she had a vivid coma fantasy involving her summer fling Danny."
If Sandy perished in the ocean, then her whole experience at Rydell High is just a wild fantasy flashing through her oxygen-deprived brain. This makes a lot of sense when you break down how profoundly weird the school is. Why is no one doing any schoolwork? How are these kids, especially the T-Birds, planning on graduating? Where are the adults?
Rydell High feels less like a real learning institution and more like a school filtered through the prism of teenagehood: It's all drama, romance, sports, and social intrigue. The characters make absurd decisions, like inviting their teacher, Mr. Murdock, to an illegal drag race. Even weirder, he's pretty chill with the whole affair.
Not to burst any bubbles, but people generally don't break out into spontaneous choreographed song and dance. Are they expecting us to believe these kids, who seemingly have zero organizational abilities, no motivation, and no professional theater training, are able to execute this kind of choreography?
If the whole movie is Sandy's fantasy - and if Sandy saw a few musicals in her life - it only makes sense that she might fantasize about her classmates being phenomenal singers and dancers. And, of course, Danny would play the role of the dashing teenage Lord of the Dance.
We all have things we would like to change about ourselves if we could. Some people wish they were taller, or thinner, or more assertive. We often fantasize about how easy life would be if we were only a little bit different. Sometimes we even dream about it.
According to this theory, Sandy gets to live those fantasies. When she shows up at the end of the movie, she has completely and effortlessly changed herself into an assertive, leather-clad vixen. She whips Danny into shape and seems completely confident in her ability to keep him in line. There's no doubt and no hesitation. It makes sense that meek and doubtful Sandra Dee would fantasize about reaching this practically unobtainable ideal.