The speaker's closing message: event sourcing turned out to be the easiest of the patterns he explored (DDD, CQRS, event-driven architecture, event sourcing). It is 'just a persistence pattern' — you store information as events in an event store. You don't need a new database, a vendor lock-in, perfect aggregates or snapshots to start. Event-driven architecture done wrong, however, can be 'really hell' because of ordering issues.