When you think about who’s responsible for all the box-office hits of the last few years—films like “A Beautiful Mind,” “Gladiator,” “The Transformers,” “Dreamgirls,” and “Sweeney Todd”—you probably picture a stout, frowning guy, puffing on a cigar, sitting in an overstuffed office chair while overlooking the hills of Hollywood. However, the time has come for us all to do some re-imagining. Replace the fat guy with a trim, L.A.-chic woman named Stacey Snider. Snider, the highly fashionable Co-Chairman and CEO of DreamWorks Studios and former CEO of Universal Pictures, recently spoke at Harvard’s Women in Business Intercollegiate Business Convention, addressing over 700 ambitious young women eager to be the next leading lady. The key to becoming the (wo)man on top, she said, was a lesson she learned in an agency mailroom—namely, “Don’t be limited by your job description.”

Snider originally intended to be a lawyer, attending law school at UCLA after finishing her undergraduate studies at UPenn. Feeling distracted, tired, and unexcited by the prospects of working in a law office for the rest of her life, she did some major re-evaluating and began working in an agency mailroom.

“I had a passion to not be a secretary forever. I was mindful of the customary career trajectory,” Snider said, “and I knew I had to do something remarkable.”

Cut to Snider’s big break: she is sitting bored in the mailroom, flipping through the latest issue of Cosmo. She calls up her friend at a publishing house and asks after any compelling manuscripts. The friend mentions that Scott Turow’s recent story about a prosecutor charged with the murder of a female colleague/lover is getting all the buzz. Snider requests a copy, reads it in one day, pitches it, writes a synopsis, and ends up pitching it again to a studio head, who recognizes her taste and drive. The book becomes the bestselling novel “Presumed Innocent,” the film adaptation stars Harrison Ford, and Snider becomes much more than a secretary.

Snider, who is known for her reliable intuition, has learned by now what makes a good film, both commercially and artistically.

“You have to have a strong idea for a hit movie, a strong core idea that resonates emotionally,” Snider said in a phone interview. “It also has to technically achieve its goal—it’s got to be well-written, well-paced, and interestingly told. For example, ‘40-Year-Old Virgin,’ at its core, sounds like a pretty funny idea. You have to ask yourself, technically, is it actually funny? Does it resolve in a satisfying way? Are the roles castable?” Universal Studios, where Snider worked before transitioning to DreamWorks, ended up investing in “40-Year-Old Virgin.”

Ultimately, the idea of a film, according to Snider’s strategy, trumps the technical execution.

“Sometimes you’ll read a really well-written script, but it could be about an idea like plumbing in the 1920s,” she said. “Who wants to see a movie about plumbing in the 1920s?”

Snider’s instincts proved right on the money when a screenplay about a racehorse landed on her desk back in 2002.

“It was a movie that had a lot of external disabilities—period, sports, the Depression, horse racing, no single star, an ensemble piece—and my colleagues appreciated the quality of the script, but were unsure about the investment. That was one I walked the plank for. I felt like it was speaking to a post-9/11 country,” Snider said. “It wasn’t just a relic or historical footnote, but rather an incredible human interest story about people prevailing against the odds.”

“Seabiscuit” became a box office hit, with an all-star cast including Tobey McGuire, Chris Cooper, and Jeff Bridges.

Snider attributes her consistency to remaining connected to the world around her. A mother of two daughters, she tries to stay hip and inspired in order to keep her outlook fresh and uninhibited.

“You need to be grounded internally and excited about the world around you,” Snider said. “If I were out of touch, it would be hard for me to know why Michael Cera is so cool.”

What audiences see when they witness an actor like Cera rising to the top of the celebrity ladder, though, is the power of a big break. In reality, people like Stacey Snider are the propellers behind the movies and stars that captivate global audiences. It takes good instincts, guts, a vision, hyper-awareness of social trends and pop culture, and excellent budgeting skills to pull off a box-office hit.

So, dispose of that image of the cigar-puffing dude in the big leather chair, because he’s probably taking orders from Stacey Snider.