When the Covid-19 pandemic began to spread across the U.S. last March, 33-year-old Shan Shan Fu noticed that none of her friends had access to adequate face masks. So in April 2020, she launched Millennials in Motion, a side hustle selling masks on Etsy. She also kept her full-time job at a consulting firm in San Francisco.

"I would work 9 a.m. to 5 p.m. at the consulting firm and 5 p.m. to 1 a.m. [on my side hustle]," she says. "For the first few months, there was no time off. I worked seven days a week, every waking minute."