It is this: The event is the captured story of business.
The way we find the big events in a movie is imagine someone says "Tell me what happened in the Fellowship of the Ring." You would tell all of, what the screenwriters call, the plot points. The major things. Again, there are different layers to the story. You can always go down a layer, later. But think of the large story plot points in your companies story.
"We get an order, we make a product, we bill the customer, we receive the check, we deposit the check" That, my friends, is a story. There are five events that occurred here. Then you start thinking of other end-to-end stories. "We discover a needed capability, we articulate that in a job description, we determine what we will pay for that capability, we advertise, we interview, we offer the position, we on-board the employee". Each of these plot points or events you should capture on a white board. Start to figure out when that event occurs, what do I know, who is involved, what products are being manipulated, when did it occur. These are the things that will make up the meta-data of your events.
Then ask, how can I capture that this occurred? Is this something that happens in a computer orchestrated process that I simply can publish that it happened? Is there a sensor that can sense the physical domain and determined it happened? Is there a way that I can determine it based on other events? Do I need to have a human put it into some UI because there are no other way, yet, to capture it? Does it come from customer, partner, information feed?
What is neat about these stories is that they are really the processes of our business. These events are the natural segmentation points in the process. So you can ask your question to go to the next layer: "What happens between receiving the check and depositing it?" This gives you more processes and more events, but more importantly, a natural hierarchy of events happens. It will also occur that you realize a story is part of a larger story. Of the ecosystems your company belongs; of the rivalry between you and your competitor. That things are occurring outside of your control that affects your story. These plot points are very important to capture.
With events, we decouple the applications. We give voice to the story outside of one application. We allow others to hear the events of the story and allow them to become another plot-line within the story without requiring the "main application" to become more complex. It allows other systems and capability to arise. To fill in gaps. To be built by others and work in tandem and be purposeful.