System behavior emerges. It is not designed top-down
No single person designed how a city works. The traffic patterns, the economic flows, the way neighbourhoods develop character — these emerge from millions of individual decisions made by people and organisations operating within their own domains, reacting to facts, expressing intent.
A well-designed distributed system works the same way. Consider a fitness platform when a class is cancelled. Scheduling publishes a single fact — the class is cancelled. Reservation reacts and cancels all affected bookings. Notifications reacts and emails every member. Billing reacts and reverses any charges. No central coordinator directed this response. No orchestrator sent instructions to each system in turn. Each responsibility reacted to a shared fact according to its own rules. The coordinated outcome emerged.
System behavior emerges from networks of collaborating responsibilities. This is not a weakness — it is the source of resilience. No single point of failure. No single point of change. Add a new responsibility — a post-cancellation survey, a space rental trigger — and it joins the network by subscribing to the same fact. Nothing else changes.
Design the responsibilities. Let the behavior emerge.