At the world premiere of “Trainwreck” at the SXSW Film Festival last March, the loudest laughs from inside the theater came from the film’s director, Judd Apatow. Slumped down in a seat behind his new star, Amy Schumer, Apatow was so invested in the story about a thirtysomething magazine journalist who emerges from a series of one-night stands to begrudgingly find true love that he actually shushed a nearby, mortified fan who tried to open a candy wrapper.

Later, Apatow and Schumer would deliver a standup comedy set in Austin that provided the launching pad for a national tour they’d announce. And “Trainwreck,” which opens today, will keep the laughs coming. Apatow, one of the most prolific producers in Hollywood (“Girls,” “Anchorman 2,” “Begin Again,” “Pee-Wee’s Big Holiday,” etc.), has been selective about his own directorial projects. “Trainwreck” is his first film since 2012’s “This is 40,” and only his fourth feature since he his breakout hit “The 40-Year-Old Virgin” opened a decade ago.

Apatow spoke to Variety about how he finds talent, his influences, discovering Schumer on Howard Stern and the perils of taking a selfie.

The tone of your movies, starting with “The 40-Year-Old Virgin,” seems to be part of every R-rated comedy now. Do you feel like other directors are stealing from you?
I never think that because I’m only borrowing and stealing from other people. For me, it was material from Garry Shandling, James L. Brooks, Barry Levinson, Cameron Crowe, in a giant way. And Kevin Smith and Todd Solondz. I loved “Welcome to the Dollhouse.” Those movies were the model for what I wanted to do, but I do it wrong somehow and it comes out more like me.

What do you mean?
I can’t pull off “Say Anything,” as hard as I try. It becomes a little different in whatever twisted way my mind works.

Do you always laugh at your own films?
I do. I’m a big laugher. I don’t get bored of jokes, and I won’t start cutting jokes because I’ve seen them 10 times and I lose touch of why they are funny. I watched “Anchorman” 150 times. I giggle every single time.

You discovered Amy Schumer by listening to her on Howard Stern.
I come at everything as a fan. I’m just like a kid who sat in his room and watched Merv Griffin all day long. So every once in a while I’ll hear something and say, “That’s my favorite comedian.” I was in my car. I was not that familiar with Amy Schumer’s standup. She was talking to Howard Stern, and she was so engaging. She was talking about her dad having MS and what her relationship is like with him. It was very dark and sad, but also very sweet and hilarious and she clearly adores him. I thought, “This is a very unique personality and I’d like to see these stories in movies.” In the middle of “Freaks and Geeks,” Jake Kasdan and I were watching Seth Rogen shoot this scene and we went, “We think he’s a movie star.” It just hit us in a flash. That happened sitting in a car listening to Amy.

Was it hard to convince the studio to cast her?
Universal Studios has been very supportive of us trying to break new people. “The 40-Year-Old Virgin” worked well for them, and “Knocked Up” for Seth and Katherine [Heigl], and “Forgetting Sarah Marshall” with Jason Segel. People always think the hook is the mega-star. But I often think the biggest hook is the person you haven’t seen before that’s completely fresh to you. People like to leave the house to see the new thing. That’s fun for me, because you get to try to figure out how someone works on screen.

You’ve helped cultivate new talent a lot, from Lena Dunham to James Franco. What makes you want to do that?
On your first movie, you’ll never work harder. People in our business work extremely hard. But there’s something about the moment, if you don’t succeed, you’ll never be able to be the star of a movie again that lights a fire under people’s asses.

How did you and Amy get started on the script for “Trainwreck”?
We worked on another idea for six months, but it didn’t feel as personal as this. And then one day I said, “I think you can come up with something stronger that’s closer to your life.”

What was the other idea?
It was a lot more high concept. I feel like what she told me about her dating life was more interesting. A lot of times you have to explain to people what they see as their boring lives is actually fascinating. If you’re just truthful, it’s very engaging.

So you don’t need to fictionalize?
Ultimately, it all becomes fictionalized. I didn’t realize it until we worked on “Knocked Up” — a little piece of behavior, the way [my wife] Leslie Mann and I talked to each other was funny, and people related to it. That’s what I learned from Garry Shandling: “The closer you are to the truth, the better the comedy will be.”

How do you send notes?
I never do any rewriting [on another writer’s script]. But we go through it line by line and kick it around and pitch ideas and jokes. We do it in chunks until we get to the end, and then start at the beginning and do it again.

The end of “Trainwreck” feels like something you wrote. How did you influence it?
Our intention was to find a way for her to evolve. When you make these movies, you want people to feel something deeply. It’s nice when people can have an emotion other than laughing.

Is Amy prepared for all the fame that’s about to come her way?
I don’t think you understand what it is until it happens. I remember Jonah Hill when he did “Superbad,” you sensed for him things that changed overnight in terms of enormous recognition the weekend after the movie opened. I think because she’s on Comedy Central and she’s touring, she’s ready for the exposure. But it’s also a drag — because you can’t just walk down the street and be goofy. Everyone wants to take a selfie.

You must get tired of people asking for them.
You have to pose with everyone and no one wants to talk to you. “Can I take a selfie?” The whole transaction takes two seconds. And if you say no, you seem like such a jerk. It also creates a thousand pictures where you look like shit. There’s always bad lighting. Or it’s at the end of the day. Or you’re drunk.