How the yield curve predicted every recession for the past 50 years

It was once just a wonky graph for academics and policymakers. But in recent years the yield curve has become a way to forecast looming recessions. News that the curve has 'inverted' can send markets tumbling, while policymakers and analysts keep a close eye on even small changes in the curve's composition. So how did this obscure graph showing U.S. Treasury bond interest rates grow into one of the most reliable recession indicators we have?