In this talk given at the FOSDEM conference in 2023, the speaker, Robert, demonstrates how to build an event-driven application in Go using the Watermill library. He explains that event-driven architecture can help address issues such as slow performance or system failures, and introduces Watermill as a solution. Watermill is a library that supports multiple Pub/Sub implementations and follows the UNIX philosophy of writing programs to do one thing well. Robert gives a live coding demonstration, showing how to build an event-driven application for booking hotel rooms, including publishing events and handling them asynchronously. He also mentions the CQRS component of Watermill that simplifies marshaling and unmarshaling of event data. Robert encourages the audience to explore the Watermill documentation and examples and invites them to an online release party for Watermill version 1.2.