That ends now. “Girls” is returning for its second season, Sunday at 9 p.m. EST. HBO’s saga of four young women living in New York will then resume, with their struggles almost certain to inspire another round of amused if pained recognition on the part of the show’s devotees.

“Girls,” of course, was created by Lena Dunham, now 26, who also stars as Hannah, a would-be but none-too-successful writer living in Brooklyn. Hannah’s circle of highly verbal, overanalytical chums includes Marnie, a gallery assistant played by Allison Williams; sexy self-absorbed bohemian Jessa (Jemima Kirke); and Jessa’s cousin, the naive motormouth Shoshanna, whose coming-of-age in the first season included losing her virginity and accidentally smoking crack.

Shoshanna has other things going on. In the season opener, she is first glimpsed in her bedroom waving a smudge stick as she thanks “the higher powers for all the gifts I have already received: a keen mathematical mind and fairly fast-growing hair.”

It’s a testament to “Girls” that a moment like this feels as authentic as it is funny.

But what does it all mean? Zosia Mamet, who plays Shoshanna with frank, wide-eyed honesty, is being grilled by a reporter for surely the zillionth time. Still, she’s game to help account for what makes “Girls” a show people talk about so passionately.

“This time period has been written about before, but in a very glossy way,” says Mamet in a determined near-whisper. “People idealize or reminisce about their 20s, but nobody tells you beforehand that it’s hard and unglamorous and often very unpleasant. What Lena has written reveals that, and it speaks to a lot of people.”

Mamet, who turns 25 next month, hastens to add that she is living a much different life from Shoshanna and company. Unlike them, she found her direction early on: “By the time I was 17,” she says, “I was in the flux of this crazy industry pushing to be an actress, which I wanted more than anything in the world.”

Nonetheless, the trial-and-error lifestyle portrayed on “Girls” resonates for Mamet and loads of people she knows as they reach the expiration date for their precociousness.

“There’s this inescapable moment in your early 20s, no matter how you get there, of feeling like everything you’ve known up until then is either wrong or doesn’t fit,” she declares, “and suddenly you’re faced with this feeling of ‘Who the (heck) am I? How do I do life? HOW is life DONE?’”

Even the characters’ well-intentioned efforts at good times are often stressful and humiliating. (And sometimes cringe-inducing for viewers, for whom “Girls,” unlike most TV shows, serves as a graphic reminder that sex between young people can be shockingly un-sexy.)

In this way, among many, does the tone of “Girls” strike a perfectly unsettling balance.

“Comedy arises out of necessity, because some things are so dark that you have to laugh about it,” says Mamet. “In this show there are very uncomfortable, very real situations that can make me cry and laugh at the same time.”

Zosia (whose name, pronounced ZAH-shah, sounds like “Sasha” with a Z) is the daughter of actress Lindsay Crouse and playwright-filmmaker David Mamet, who split, she says, “when I was a zygote.” He then married actress Rebecca Pidgeon.

Acting, therefore, “is the family business. I grew up backstage and on movie sets, and I thought they were the most magical places on Earth. But my dad, who was always very supportive, never pushed me in that direction. In the same way kids from non-artistic families who want to be actors might be told, ‘Well, that’s odd, but whatever makes you happy is OK,’ if I’d wanted to be a veterinarian, I think my dad would be like, ‘That’s odd, but OK.’”

Veterinary medicine’s loss was acting’s gain. But it wasn’t easy breaking in. Endowed with heroic dark eyebrows she pumps thoughtfully when working through an idea and a smile that, when deployed, could outshine Julia Roberts’, Mamet is no off-the-rack actress, no standard-issue starlet.

She remembers all those casting sessions, when “the look on those people’s faces was one of confusion: ‘What WAS that?’ Sometimes a director or a writer or a casting director would fight for me, but the producer or studio executive would be like, ‘No! We can’t sell her.’”

She was undeterred. “My father always said, ‘Don’t listen to anything after “No,” because they don’t know what they’re talking about.’”

And sometimes they said yes. She landed roles on “Parenthood,” ”United States of Tara” and “Mad Men,” as well as the acclaimed indie film “The Kids Are All Right.”

Now, during the “Girls” hiatus, she has just begun rehearsals for an off-Broadway play.

Opening on Jan. 31, Paul Downs Colaizzo’s raw comedy “Really Really” casts Mamet as one of a cluster of friends caught in turmoil the morning after a wild party.

It is for her role in this, her first play, that Mamet has abandoned her native brunette and gone blond.

“I had never dyed my hair in my life,” she says. “The idea of dyeing it for the first time when I’m doing a play for the first time felt great!”

“Really Really” is scheduled to run through March, and not long after that she expects to be back shooting next season’s “Girls.” She’s eager to continue exploring Shoshanna.

“I still have no idea who she is,” Mamet says with a laugh. “All the characters on ‘Girls’ are growing and changing, which is how real people behave, especially when we’re young, trying to figure out who we are, doing things that are the polar opposite of our characteristics.”

Thus has she put her finger on another thing that gloriously sets “Girls” apart: its reliable unpredictability that keeps the audience surprised, off-kilter and, yes, talking.

“So often in film and television the characters are stuck in boxes,” Mamet says. “But that just isn’t real. On our show, we’re often playing against type and stepping outside of our boundaries. That’s what people do.”

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