Every part of a story contains the DNA of the whole. An example of this can be found in two John Travolta dance sequences: one from Saturday Night Fever and the other from its sequel, Staying Alive.
[youtube https://www.youtube.com/watch?v=LUID0jSh2Ic]

Here is a dance scene embedded in reality. Tony, sick of fencing with his dance partner, decides to take over the floor. It’s clear he’s done this before, and that within the confines of this small pond, he’s the biggest fish. He puts on great moves, and the movie gives us space to see them, but I can imagine that any talented amateur could do what Tony does if he put the rehearsal time in. He’s good, but he’s not unrealistically good. What also comes through is Tony’s love for disco dancing. It is, as he later acknowledges, the one area where people think he’s worthwhile. He knows it can’t last, and he’s afraid of what comes after, but right here and right now, he’s reveling in it.

Staying Alive is, in so many ways, a different story:
[youtube=://www.youtube.com/watch?v=ELttkHLU4vc&w=560&h=315]
Okay. Ostensibly, this is a Broadway show, and Tony, an understudy, is now the star. Of course, it’s hard to believe that the on-stage proceedings are part of a Broadway show, what with the frequent intrusions of stage fog obscuring the dancers’ feet–and often most of the rest of them–and the use of prerecorded tracks instead of live musicians and singers. The dance moves here are generic 1980s cheese, which looked better when they were part of deliberate cheese fests like the opening of “The Running Man” TV show in The Running Man. (And I must say I liked the flying kick move a lot more when David Lee Roth did it in Van Halen’s “Jump” video.) The sequence is cut in such a way that it’s easy to forget that all these images are supposed to have some kind of continuity. It does emerge that there’s one dancer who likes Tony, and another that Tony dislikes. But Tony overall feels less real here. He’s certainly sweater, and he’s cut like a julienne salad, but there’s little sense of him as a person. He’s executing moves, but there’s no sense of why he felt they needed to be executed.

The whole movie’s like that, really. That’s why it’s considered one of the worst sequels of all time. It’s also why devoted fans of Saturday Night Fever, like me, ignore it.