"We were spending $180 a month or so on diapers, which seemed nuts. And the subscription model made sense," says Abby & Finn cofounder.

"Earned media and public relations coverage is more influential for D2C brands," says Satya Menon, managing partner, ROI Practice, Kantar.

Many D2C brands succeed because they help eliminate the pain points or friction that behavioral economists simply call sludge.

Founded in 2011, mattress seller Saatva is not only a long-term survivor, it's profitable.

Airbnb announced a dramatic increase in its luxury travel offerings -- and a campaign to "bridge generational divides within the LGBTQ+ community."