"On a daily level, I don't like 75 percent of the things I do. That's the weird part of being a startup founder." 

Max Nussenbaum, co-founder and CEO of property management software company Castle, says these words in the new documentary, "Generation Startup." It's the dead of winter. Nussenbaum, dreading calls he has to make to investors, is in a heatless Detroit house he's renovating with his other Castle co-founders. Later in the film, we see him working out of a tent he set up in the living room because of the extra insulation it provides.

"Generation Startup," which has been playing at the Detroit Film Theater, doesn't glamorize the life of those who work at or found startups. The movie follows four people enrolled in Venture for America (VFA), an organization that places recent college grads in startups from cities with lower rates of entrepreneurship—in this case Detroit. Former VFA fellow Nussenbaum and Brian Rudolph, founder of the chickpea pasta company Banza, also feature heavily.

It should come as no surprise, but starting a business is hard. As such, doubt is one of the movie's major through lines. 

Early in the film, Rudolph and VFA fellow Avery (we're only told the fellows' first names) recount a mistake that could have been fatal for the business. As Banza scaled up production, they failed to account for changing variables by moving to a factory. The error resulted in 13,000 pounds of faulty product and a failed pitch meeting with a major gourmet food store, Papa Joe's, during which the prepared pasta turned to mush. 

"I've never built a company before," Rudolph says. "I sometimes feel over my head. That's when it's really tough."

Kate, who's placed in the tech company Detroit Labs, makes networking with other women in tech her passion project and starts a group, Women Rising. During a conversation with a potential mentor, Kate wonders how it's possible to juggle starting a family and a business. "Where does time appear?" she asks.

The answer: it doesn't.

The movie begins with a frank conversation between one of the fellows, Labib, and his parents from their home in Yonkers, New York. Labib's parents, who are from Bangladesh, urge him to take a secure job in the pharmaceutical industry. 

"Do you think people should do what makes them happy?" Labib asks.

"Uh, no," says his father, who works nights as a limo driver.

The irony is that none of the 20-somethings in "Generation Startup" appear to be having much fun, whether they're working from a freezing house, waking up at 5 a.m. to sell pasta at Eastern Market, or staying up multiple nights in a row making calls to a factory in China. All this work means they have no time for socializing. "In reality, it's not fun," Avery says.

"I'm putting all my energy into these things and there's nothing left internally," Nussenbaum says.

Dextina, who's placed in Rock Ventures and is African-American, finds herself isolated at work. "Most of my friends in startups are white men ... I struggle to be myself."

But there's an important difference between having fun and being happy. All the late nights and early mornings put into these startups pay off in gratifying ways—these millennials don't have it easy, but they come out better for it. VFA founder Andrew Yang says in the film that doubt is essential to developing character and values. 

Model D recently covered the incredible success of Castle, which was accepted into the prestigious Silicon Valley startup accelerator Y Combinator and received hundreds of thousands of dollars in investor money. Banza now employees 32 people and is sold in over 2,000 stores. They also got to pitch Papa Joe's a second time—with much better results.

Rudolph is grateful for the trials he was put through. "I'm glad that it's hard at the end of the day ... it means it's also hard for someone else to make this product," he says.

"Generation Startup" doesn't glorify startup life. The workload is unforgiving. Breaking in as a woman or minority presents its own challenges. Detroit is still miles behind Silicon Valley and Seattle in its support for startup infrastructure.

But the movie also proves that it's possible to build and scale a startup here. And the personal and financial rewards are potentially great.

"Generation Startup" is playing at the Detroit Film Theater through Saturday, October 15.