He's mad at the finance industry.
"I'm angry," he tells PEOPLE at the New York City premiere of the upcoming film, The Big Short, which Pitt produced and plays a supporting role in. "I'm angry that so many people lost their homes," he adds.
The Big Short tells the true story of a group of outsiders who see the 2008 real-estate crash coming, and when they bet against it, they win big.
But Pitt is aware that not everyone who lived through the economic crash was as lucky as the guys in the film.
"Families were put on the street, they lost their life savings, and yet no one was held accountable," Pitt says. "No senior official was held accountable. That's amazing."
Not only is Pitt angry, but he's fearful for the future. "There's something seriously wrong, you talk to the experts now and they say nothing's changed. The entitlement to make money without responsibility still exists, it's alive and well. And the same practices are still going on, only in different arenas. But nothing's changed," Pitt warns. "That's a problem."
How does Pitt know so much about finance?
While he's no banker, he did learn a thing or two from the book on which the film is based. "It wasn't the film, it was Michael Lewis' book," Pitt tells PEOPLE of getting a crash course in finance thanks Lewis' 2010 novel, also titled The Big Short. Lewis also wrote Moneyball which was adapted for the screen in 2011 and also starred Pitt.
"It was helping me understand it, because it's so convoluted and so complex and it's designed that way so the applicant doesn't know what they're getting into, and that's a problem," Pitt says.
In the film, Pitt plays a retired trader – and while the actor, who turns 52 this December, is far from retiring himself, he says the best thing about growing older is that, "you just get more and more chill."
And his costars certainly have no complaints working with a pro like Pitt. Finn Wittrock, who plays a hedge fund founder turning to the retired trader for advice, admired Pitt's professionalism.
"Our first day of shooting, there was like a long phone call we had with him, so he was not on camera," Wittrock tells PEOPLE at the premiere. "Lots of actors would have the [assistant director] read those lines but he sat behind the camera all day with us and read the other end of the phone call and played and improvised."
"He's always like, I'm here for the other actor. It's make all the difference in the world," Wittrock says.
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Apparently, Pitt's also a lot funnier than people may realize. "He's really funny, not everyone knows that. A lot of his improv is in the movie," Wittrock says of the By the Sea actor.
Also starring Steve Carell, Ryan Gosling and Christian Bale The Big Short opens in limited release on Dec. 11 and hits theaters nationwide on Dec. 23.