The Marvel Cinematic Universe did what some might consider the impossible, and it paid off with Avengers: Infinity War.

Over 19 movies, the Marvel Cinematic Universe has brought in over $6 billion and counting for Disney. However, with that said, Avengers: Infinity War co-director Joe Russo said that other studios should beware when attempting to try to create their own cinematic universe.

Russo was talking to Variety about Avengers: Infinity War, which shattered records with a $257.6 million domestic opening weekend and is already at $905 million worldwide. While Marvel has five movies that broke $1 billion worldwide each and a sixth that will do so this weekend, he said that it is a huge gamble.

“Not everything can be sustained through a cinematic universe,” Russo said. Instead, he said it is “a function of audiences craving new kinds of storytelling.”

It is clear that it doesn’t always work. The Universal Monsters had their own shared universe back in the ’30s that was incredibly successful. However, when they tried to revive it with new monster stories — first with The Wolf Man and then with Dracula Untold and finally with The Mummy, people just shrugged their shoulders.

Marvel has something special going.

For one thing, the company has hired great directors (Jon Favreau, Kenneth Branagh, Shane Black, Joss Whedon, James Gunn, etc…) and then had them make movies that remained true to the spirit of Marvel Comics.

They also did something unique.

So many non-fans complain that “comic book movie fatigue” will set in, but that is the same as saying “horror movie fatigue” or “rom-com fatigue” will set in. See, Marvel has made action movies (Iron Man), sci-fi space movies (Guardians of the Galaxy), heist movies (Ant-Man), political thrillers (Captain America: Civil War) and fantasy movies (Thor).

Avengers: Infinity War mashed all that together in one giant film.

Yes, they all have superheroes but they are different genres of films. Comic book movie is NOT a genre. Because of that, Marvel can bring back beloved characters and create something different for them every time out.

Joe Russo also said that it is important to keep surprising viewers, which is why Marvel likes to send out misdirection and keep things very secretive. It helps to keep people excited and wanting to see more.

Other studios want to create shared universes (King Kong and Godzilla) is in the middle of starting their own), but they need to do more than just put the two monsters in each other’s movies without creating something special at the same time.