Last year, Stephen Thorpey was a successful ad salesman working at a large New York media company, itching to start his own business but feeling apprehensive about the economy. The tipping point to launch his own firm came from an unexpected place: Browsing the Web one day, Thorpey read an inspirational poster called the Holstee manifesto.

“I had been wanting to go off on my own for a while, but there was a risk associated with it,” Thorpey said. “Seeing that manifesto for the first time was almost a nail in the coffin for me...I decided to live by those words.”

The manifesto reads like something out of a self-help book: A 15-sentence message comprising brief commandments such as, “Do what you love and do it often,” “If you don’t like your job, quit,” and “Travel often; Getting lost will help you find yourself.”

The Holstee manifesto is the most iconic product of the Brooklyn-based apparel company Holstee. Although the company was founded with the aim of selling sustainably sourced consumer goods, the poster of the manifesto is now one of Holstee’s best-selling items. At one point this summer, they sold out of it with a four-week back-order. The manifesto has been translated into 12 languages, and by Holstee’s own approximations, it’s been viewed more than 50 million times.

Surprisingly, it was the one thing about their business they never intended to become popular.

Holstee was founded by brothers Dave and Mike Radparvar and their friend Fabian Pfortmuller in 2009. Before that, Dave and Mike were, like Thorpey, successful in their careers but growing restless in the corporate world. They began tinkering with various side projects in their spare time until they finally came up with something they thought had staying power: A T-shirt with a side pocket positioned like a holster, or a “hols-tee.

“Even though all our friends were plowing forward with digital ideas, the idea of having a tangible product was appealing to us,” Mike Radparvar said. “There’s been no real innovation behind the form of a T-shirt, and we thought it would be neat to rethink the T-shirt in general.”

Dave and Mike made a pact that they would both quit their jobs on the same day to work on Holstee full-time.

“You know in ‘The Matrix’ when they unplug you? It felt like that,” Radparvar said about quitting. “We had this nervous energy and excitement.”

They went into survival mode, cutting expenses by renting out their apartment through the site AirBnB and cooking at home. They joined up with Pfortmuller, and between them they had just enough to bootstrap Holstee.

The trio set out to produce and sell only environmentally conscious products. The original Holstee T-shirts were made from recycled plastic, and the company’s “upcycled” wallets, made from plastic bags, are bought from an organization that works with Indian “rag-pickers” in Delhi. Ten percent of their sales go to the micro-finance lending organization Kiva. To codify their ideals, they wrote the Holstee manifesto, put it on their Web site and — largely — forgot about it.

“We did a lot of things with the intention of them going viral, but we never expected this,” Radparvar said. Among other gimmicks, the company tried a Ho-Ho-Holstee hotline, a holiday-themed campaign in which people could call and ask questions about where to find certain gifts. It didn’t really catch on. “If there’s one thing that people picked up, I’m glad it was the manifesto.”

Eventually, the manifesto was posted on the social blogging site Tumblr, and made its way through social networks and blogs from there. In March of last year, a Boston designer named Rachael Beresh stylized the manifesto for printing on posters and on greeting cards made from elephant dung.

“When we started producing the Manifesto poster, we worked with one letterpress printer part-time,” Pfortmuller said in an e-mail. “Now we work with two producers, and one of them has hired an extra person to keep up with the strong demand.”

Radparvar is pleasantly surprised when people thank him for the manifesto. “It’s as if no one told people that you should be enjoying life,” he said. “Maybe you just have to see something lots of time to act on it.”

Last week, Holstee released a video featuring New York city cyclists saying lines from the manifesto. Thorpey, an avid cyclist with roots in the New York bike scene, volunteered to help find the video’s “stars” and to distribute it through his networks and through social media. The video has since been viewed more than 70,000 times.

“I’m so grateful for the impact that the poster has had on my life and the success that I’ve found since then,” Thorpey said. “I wouldn’t ask for anything in return. If they have this impact on me, why can’t they have it on another entrepreneur?”

Scott Rick, a professor of marketing at University of Michigan, likens the manifesto to the “Just Do It” slogan popularized by Nike. The difference, Rick said, is that Holstee explained what the “it” is.

“‘Just do it’ got people buying shoes, leaving bad marriages, asking people to prom,” Rick said. “This company seems to be very credible and genuine, so it’s a familiar message but from a more sincere source.”

Holstee’s success also signals a shift in the tastes of consumers — and consequently, how small businesses are marketing to them.

“People do look for meaning in a different way in the things they buy now,” said social business strategist Olivia Khalili of “They want to feel like, ‘my products can do more than just be a product.’”

A 2010 survey by Opinion Research Corporation for the Cone Communications firm found 41 percent of Americans said they bought a product because it was associated with a cause or issue in the last year — double the number who said they did so in 1993.

That said, few companies succeed in simply selling their tag lines emblazoned on paper. Rick said Holstee’s transparent feel and inspirational message could help them boost sales of their other products, as well.

“If people are choosing between Urban Outfitters and Holstee, Urban Outfitters might be seen as more of a corporate entity,” he said. “This lets people get a similar product but with less guilt.”

Holstee’s current product line is fairly limited, leading Khalili to wonder whether the company’s word-of-mouth marketing outpaced their supply. Many of the company’s pendants, shirts, scarf-like “neck fins,” baby bibs and aviator sunglasses are currently sold out.

Radparvar isn’t concerned, however, saying the company plans to launch several new products in time for the holidays, including a black faux-fur wallet designed in partnership with PETA and new T-shirts made from hemp fabric. They also plan to collaborate more with other designers on products sold in their “Curated by Holstee” section.

One thing the company isn’t selling: bicycles. The decision to feature cyclists in the manifesto video wasn’t a product marketing ploy, which led to some confusion when the video was first released.

“People were saying, ‘This is a really amazing video, but what the heck is Holstee?” Radparvar said. “We just love riding bicycles. It’s part of who we are.”