There are occasions where you want an event listener node to listen to an event only if other prerequisites have been made or another event have been called first.
This is best achieved by using sub-graphs. An event listener node inside of a sub-graph gets only triggered when the sub-graph is currently active.
So for example lets assume we have an Event listener node (A) in the root graph which is connected to a sub-graph. Inside of the sub-graph we have another Event listener node (B). This way, event listener B will only listen if event A has been called first.