Amy Errett wasn’t the likely candidate to reinvent women’s haircare. For one thing, she doesn’t color her hair. For another, she’d never built a company shipping physical goods before.

And this wasn’t lost on her high-powered Silicon Valley network, who couldn’t quite understand why someone so “smart” was wasting her time on such a frivolous category. One they (Usually men whose wives could easily afford $400 salon treatments) just didn’t “get.”

Instead of listening to the Valley elite, Errett listened to her nine-year-old daughter who’d heard her ask countless family friends about their hair routine, whether they colored it, what they used, if they were concerned about the toxins in those treatments, the ammonia that could burn a hole in a...