You don't have to explain to Ryan Coogler why people of every age, race, gender and nationality run up the Rocky steps.
Coogler, an African-American man born and bred in Oakland, Calif., inherited his "Rocky" love from his father, who inherited it from his mother - three generations have found the movie a source of powerful, personal inspiration.
"My dad watched my mom pass away from complications of breast cancer," Coogler said. "Near the end, the only thing they could do together was watch TV, and it so happened the "Rocky" movies were on a lot, and that became a deep bond for them."
His father coached Ryan in football, and used the movies as a motivational tool.
"I'd watch with my dad before a big game, and we'd get fired up every time, we'd go through the full gamut of emotions, every time," Coogler said.
Then it all came full circle - Ryan's dad became ill, just as the young director's success with "Fruitvale Station" was cresting, and the two returned again to the movies that sustained them in football locker rooms and hospital waiting rooms.
Coogler channeled all those emotions into his script for "Creed" - Rocky battles sickness and despair, even as he helps the son (Michael B. Jordan) of foe-turned-friend Apollo Creed find his way in the ring, find his way in life.
"That's what the story represents to me," he said. "That's the story I wanted to tell."
Talk to Coogler for five minutes about his passion for the film, you understand how he coaxed a reluctant Sylvester Stallone out of "Rocky" retirement.
Stallone is glad he returned, and has been effusive in his praise for Coogler, who returns the favor.
"Here's the amazing thing about Stallone. He's nothing like the character of Rocky, or Rambo. He's intellectual, eccentric - an artist. That's when you realize what an incredible actor he is - to make us think those guys are real."
Stallone responded to Coogler's personal, emotional vision, because that's always been his relationship with the films, all six of them.
"In talking to Sly about it, each of those films is about his life, and how it changed in relation to the success of the movies, how it reflected his relationship with the film industry."
For Coogler and for Jordan, "Creed" performs some of the same functions. Both grew up in modest circumstances - Jordan in a Newark, N.J., home where the family used the oven for heat in the winter.
Both have found success in movies, but their perspective on money, fame, identity remain informed by their humble upbringings.
And that's the story of Adonis Creed in the film - raised in foster homes, adopted by his wealthy stepmother, not sure where he belongs, caught between two worlds.
"It can be hard for people who experience on both sides of that divide," Coogler said. "There are people who want to put you in a box. And that's true of Adonis - he doesn't really fit in anywhere. It has to do with why he wants to fight so much. He's fighting to be accepted for his place in the world."
Coogler saw the original "Rocky" as a story of a man's personal growth, and a love story.
"What's crazy about the film is that while it has spectacle that gets your blood rushing, there are really only two boxing scenes in the movie. The rest of it takes place in bedrooms and locker rooms and pet shops," said Coogler.
Speaking of pet shops, Coogler understands the importance of the Adrian/Rocky element. In "Creed," Adonis falls for a Philly singer named Bianca (Tessa Thompson), a fighter in her own way, in her own arena.
"To me," Jordan said, "it represents what young love is like in 2015. It's two people with independent dreams and goals who recognize that in each other. They push each other, and that drive and that focus brings them together. Bianca's not a character who's just there to support Adonis. She's got her own thing, and it has to go both ways."
"Creed" also reflects Coogler's enthusiastic feelings for Philadelphia, a city he fell in love with long before he started writing his "Rocky" spin-off.
"I first came here when I was 16. My first [football] recruiting trip was to the University of Pennsylvania. For someone who was looking at the city through the lens of a West Coast kid, the city was a trip. How old everything is, how steeped in history."
The city he found when he returned for "Creed" pleased him even more.
"Here's what blew my mind - how diverse the city is. Culturally, religiously, in every way. And everybody kind of mixes, you see different groups, but the same styles. There's this cultural bleed that happens here that is very interesting to me. Philly slang - white dudes, Asian folk, black folk, all using the same kind of language.