New Zealander and former pro soccer player Tim Brown hung up his cleats in 2010 after going to the World Cup. His next move surprised everyone: He set out to make simple shoes that looked nothing like the ones he was paid to wear as an athlete. He teamed up with biotech veteran Joey Zwillinger to re-engineer the running shoe out of wool. Here, Brown and Zwillinger describe how, after eight years and many prototypes, Allbirds has become a cult brand–especially in Silicon Valley–by keeping things simple. Read the interview at Inc.