Last summer Michelle Lam spent two hours in the lingerie section of a San Francisco department store trying on "20 different bras, one after the other, in what seemed to be a random trial-and-error sequence," she recalls. She ended up leaving empty-handed, but the experience sparked an idea: an online bra store where women could find the perfect fit.
Lam, 33, is no fashionista, but she understands how to build a business. As an accountant at PricewaterhouseCoopers, a research associate at the Boston Consulting Group (BCG), and an associate at Parthenon Capital, she saw firsthand the different facets of how companies work. At BCG, she contributed research to a book featuring a Victoria's Secret case study. In 2007, Lam was made a principal at Bain Capital Ventures -- the first female principal in that arm of the firm. One of her early assignments was to evaluate LinkedIn's prospects as the startup raised its Series D funding. Beginning in 2010, Lam spent five months helping Rent the Runway -- a dress-rental website with fewer than 60 employees at the time -- structure its customer-acquisition plan.
In 2011, Lam left Bain, moving to California when her husband began a fellowship at the University of California at Berkeley. She took time off, developed an itch to start something new, and soon after found herself frustrated in that department store.
A friend set her up with Aarthi Ramamurthy, a 28-year-old former program manager at Microsoft. The two developed a personalized quiz based on the rules that experts use to fit customers without a tape measure. The co-founders hosted bra-fitting parties in Lam's living room. Over champagne and sushi, guests filled out quizzes and tried on bras based on their results. (A professional fitter was on hand with a tape measure to check against the quiz.) True & Co. released a beta version online in January 2012, and officially launched in May. In 36 hours some 20,000 women had signed up for its services.
Lam says she hopes to use technology to revamp a customer experience that has been "the same since the modern bra was invented in the mid-1930s." True & Co. has raised $2 million in seed money. Aileen Lee, a partner at Kleiner Perkins Caufield & Byers, has invested, citing market potential (intimates are an estimated $9 billion market in the U.S.) and Lam's intensity.
Ready for launch
Risk career, not relationships. "You will always be employable," Lam says. Professionally, entrepreneurialism will only help. The real risk is not your career, she cautions, but personal relationships.
Don 't listen to everyone. Negative reviews are inevitable. "Listen to those who support you," Lam says.
Downsize. She and her husband downsized after leaving their venture capital jobs. "Before you take the leap, make a budget," Lam advises.
This story is from the October 8, 2012 issue of Fortune.