Mirror Entrepreneur Sold Her Fitness Startup to Lululemon. Letting Go Meant Sticking Around.

Brynn Putnam, a former ballerina, knows something about pivoting. That skill was put to the test this year when the 37-year-old entrepreneur finally got a boss.

Ms. Putnam created the Mirror, an at-home fitness product that streams workout classes to a reflective glass propped against the wall. As the pandemic increased the demand for such gadgets, Ms. Putnam adjusted by deciding to sell Mirror to Lululemon Athletica Inc. for $500 million.

Ms….