Ever feel terrified before you go on stage?

Sure, sometimes I just think I’m going to vomit. But there’s something about knowing you have to do this thing and it’s your responsibility that makes it doable. Some part of your brain tells you that you can handle it, and once you get on stage, it’s really fun.

The play begins at a drunken college party where your character, Leigh, has sex with one of the rich college guys. Even at the end, we don’t know whether she seduced him or was raped. Do you?

One of the extraordinary things about the play is that it’s so ambiguous. I’ve read the play a hundred times, but every night there are moments when I hear a line and understand it differently. It’s rocked with tiny land mines. All of us in the cast have different ideas of what we think happened, and even our ideas change. We talk about it all the time, and we’ve done our job if people leave the theater still unsure.

Your character is a girl from the wrong side of the tracks who uses sex and lies to survive and advance herself. Is that OK?

It’s such a complicated question. The interesting thing is how the play challenges people’s idea of a moral compass. My character feels that throwing this boy under a bus isn’t a wrong she’s doing—it’s righting the wrongs done to her. People have different ideas of what justice is, and their moral compasses are calibrated in different ways. To our generation, right and wrong are very subjective.

The play—and Girls—suggests that everyone in your generation is out for themselves. Agree?

My generation has been stamped with the image of being selfish. Perhaps, but I’d also say we’re a product of our upbringing. We’re the ones who were taught to believe that you get a trophy just for playing. The effort to boost children’s image of themselves has created a lot of people in their 20s who don’t know how to deal if they don’t get what they want. But there’s a positive side to that too. You can argue that our whole country was based on the idea of being given every opportunity and making of it what you will. It has created interesting human beings.

Sex isn’t very sexy in this play or in Girls. Is that sad or just honest and realistic?

It’s absolutely true. When you’re in your 20s, sex isn’t sexy 90 percent of the time. You’re trying to figure out who you are and what you want out of relationships, and when you put people together in that space, it’s rare to have an encounter that’s sexy and polished and wonderful. It’s more likely to be scared and timid and awkward. Sexuality is complicated and overwhelming to young minds.

I filled our whole time off with the play, and I’ll probably take that one free week and totally fall apart. But you know what? I’m not complaining. I’m so lucky to be doing this.

You’ve gone from virgin to slut. Shoshanna never had sex before, and your character in the play has sex with anyone. Which do you prefer?

Oh my god, that’s funny. I don’t know. It’s apples and oranges. But none of it is Sex and the Citysex.

You were on Jimmy Fallon recently, and all people could talk about afterward was how much cleavage you showed. Was that a plan to change your Shoshanna image?

It was a dress by my all-time favorite designer, Carven. I was not making a statement! I’d wear anything Carven lends me, and that was really just a dress I like. Nobody had any idea it would cause such hoopla.

How odd is it for you that suddenly everything you do or wear gets discussed?

It’s exceptionally bizarre. I’m trying to handle it day by day. People come up to me all the time now to tell me their stories about sex or boyfriends. Some of them are pretty funny. I wonder if thinking of me as the character from this play will make them not want to talk to me anymore. But since all of this is a result of the success I wanted, I’m actually grateful for it.

Speaking of success, you looked completely stunned when you were onstage at the Golden Globes.

Oh my god, it was beyond shocking. Just the fact we were there was insane. A year and a half ago we were shooting our first season of Girls, and even to be nominated for a Golden Globe was mind-blowing. When Lena [Dunham] won the first time, I thought it couldn’t get any better, and then to win [for Best Comedy Series] and have our show honored was surreal. It was like being shot out of a canyon.

How is Shoshanna changing in the second season?

She’s growing up a lot. She’s trying to figure out what she wants as opposed to what she thinks she’s supposed to do. I’m not positive what kind of reaction we’re getting because I don’t read reviews. But I think people are liking it.

Most of your fellow cast mates recently graduated college. Ever regret not going?

I never regretted it for a minute of my life. I knew what I wanted to do, and college just felt like a detour. For some people, those four years in college are important, but I just happened to hate school and I wanted to start working so badly that I wouldn’t even fill out an application after high school. I would tell people who want to act that there’s no better place to learn than in the theater or on a movie set.

How were you so certain about what you wanted?

I just got lucky. I was very determined and ambitious, and ready to do what I had to do. I was born with a passion, and nothing makes me as happy as acting.

Really Really has very similar themes to the play Oleanna by your father, David Mamet [the Pulitzer Prize-winning playwright]. Both are about sexual power and manipulation. Did that connection appeal to you?

It was just coincidence that I got offered this play. But I agree—when I read it, I thought, “Wow, this is a lot like Oleanna.” Maybe I’ll be in that one someday. Who knows. Life is long. He hasn’t seen Really Really yet but he’s coming opening night

That’s got to be a big deal. David Mamet in the audience.

He’s just my dad.

How do you feel about his recent right-wing political views?

I don’t talk politics with my dad. We stick to life in the movie business.

Well, politics or not, if I were Lena Dunham, I’d at least be giving you scripts to run by your dad.

It’s never happened. Lena knows what she’s doing. She’s very focused. Honestly, I don’t think she needs help from my pop.

Lena is dating the guitarist for Fun. and has made a point of saying it’s OK to talk about being in love. Anyone you’d like to talk about?

I’m not dating anyone right now, so there’s nobody to talk about. And whether or not you should discuss it depends on the person and circumstances. Lena is really proud of Jack [Antonoff] and they’re both wonderful human beings.

When you’re finished as Leigh, do you go right back to the set of Girls?

If the play gets extended—and knock wood it will—we’ll go to the end of March. Then I’ll have a week before we start shooting Girls again in April. I filled our whole time off with the play, and I’ll probably take that one free week and totally fall apart. But you know what? I’m not complaining. I’m so lucky to be doing this. I learn my lines and show up on time and hope it all keeps going.