'Treat your business partnership like your marriage'

Allbirds is an ecological shoe brand from California which uses wool and tree fibre instead of leather.

The company sold a million pairs within two years of launching. But even while business was booming, the two founding partners realised their relationship was in crisis.

Co-founder Joey Zwillinger discovered that working on the partnership was as important as working on his marriage.

Video journalist: Jeremy Howell

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