Since 1976’s “Taxi Driver,” filmmaker Paul Schrader says he has been looking for certain problems that he could place within a metaphor. In that case, he says, “It was a young man’s sense of loneliness, and the yellow taxi car was the metaphor. And I’d put the two together to create sparks and see what happens.”

He does it again in his latest movie, “The Card Counter,” which bows at the Venice Film Festival Sept. 2. This time, he wanted to do the story of someone in purgatory — the casino circuit was the perfect setting. “When was the last time you saw someone laughing there?” he asks. The film follows William (Oscar Issac), a veteran who served at Abu Ghraib. He is also a lonely and tortured soul.

“I discovered when I put the metaphor and a problem next to each other that this was a man who would have been punished by the U.S. government,” Schrader says. “But he still feels he hasn’t been punished enough.” William lives a life of self-punishment, waiting for personal redemption.

Guilt is something Schrader is used to. “I grew up in the Christian Reformed Church that said, ‘I’m terrible, you’re even worse.’ I have a background, even if I don’t believe, that predisposes me to invite guilt as the gift that keeps on giving.” Schrader continues, “When I see a truly guilty person, like this, in real life, they’re full of fabrications and they’re trying to explain to you how they didn’t do anything bad, and the media is deceptive. My take is, I did something bad and you think you’ve punished me? You haven’t. I’m still punishing me.”

Schrader, who received his first Oscar nomination for original screenplay for 2019’s “First Reformed,” says, if you’re able to tell a story for 45 minutes and it keeps someone interested, you have a movie. “I don’t start writing until I know, pretty closely, what will happen on every page.”

Schrader also says he doesn’t do much research, only what’s necessary. “I’ve never driven a taxi cab. I’ve never been a social escort and I’ve never been a professional poker player. I know enough to get by.”

The film also stars Tiffany Haddish, breaking away from comedy in her role as La Linda, a middleman, agent and pimp. It’s not the first time Schrader has cast a comedian, going against type.

He cast Richard Pryor in “Blue Collar” and most recently, Cedric the Entertainer appeared in “First Reformed.” “It’s great for these comedians. They want a chance to say, ‘I can do things other than stand-up,’” says Schrader.

Haddish was eager to learn from him. “The best lesson I could give her was not to be too needy and not be thrown if something’s not working. You’re not going to get thrown in a movie because you have a director and a story to protect you. You’re not out there alone.”

When COVID shut his movie down with 80% already shot, he admits he was worried the film would not see the light of day. With six scenes left, he started putting the film together with still images and placeholders. “I could show it to people and ask, ‘What am I missing?’” One of those was Martin Scorsese, who is credited as an executive producer. “That was the upside of the hiatus, that I could go back and have the luxury of Marty.”