So… the Shia. What makes them different from their Sunni counterparts?

The textbook explanation for the difference between Sunni and Shia is almost always the succession of Muhammad after his death and whom each side supported. It’s correct, but it’s really just a starting point. I start this episode talking about the commemoration of Husayn’s martyrdom at Karbala – because that’s really the birth of the divide – when Shia became an actual thing.