Robert Downey Jr. and Mark Ruffalo didn't always understand what was going on in those Marvel movies

• Robert Downey Jr. and Mark Ruffalo were sometimes confused by the Marvel movies they starred in.
• The pair appeared in several "Avengers" movies together.

Robert Downey Jr. and Mark Ruffalo didn't always understand what was going on in the Marvel comic book movies they worked on together.

Downey's career was revitalized in 2008 when he starred as Tony Stark in "Iron Man," while Ruffalo replaced Edward Norton as Bruce Banner in 2012's "The Avengers."

The pair subsequently appeared in three other "Avengers" movies together, including the box office behemoth "Avengers: Endgame," which earned $2.799 billion worldwide.

Ruffalo and Downey looked back on their time in the Marvel Cinematic Universe in a conversation for Variety's "Actors on Actors" series, and admitted that the superhero scripts were sometimes lost on them.

"And then we had this whole decade-and-a-half Marvel run where we were just looking at each other like, 'God, we're really lucky. What are we doing? Who's a wizard? Who's coming from outer space?' which I think was another great challenge," Downey said.

Ruffalo also noted that he had doubts over being cast in the MCU.

"It was such a different world. They didn't really cast people like us," said the actor. "I'll never forget, I was like, 'I don't know if I'm right for this.' And you're like, 'Come on, Ruffalo, we got this.'"

It isn't just actors that can get confused about the events of the MCU, as "The Marvels" director Nia DaCosta told Vanity Fair in September that she didn't understand some of the scenes she was shooting.

"Sometimes you'd be in a scene and you'd be like, 'What the hell does any of this shit mean?'" she said.

DaCosta also admitted to feeling frustrated filming scenes that would later be finalized using visual effects.

"Or an actor's looking at some crazy thing happening in space, and they're looking at a blue X. There were obviously hard days, and days where you're like, 'This just isn't working,'" she said.