In most cases, an event needs to travel through all of the cables leading up to a node before it can reach the node itself. (The one exception is the node that starts and ends a feedback loop, since it has some cables leading into the feedback loop and some coming back around the loop.) A problem can arise if the nodes and cables in a composition are connected in a way that makes it impossible for an event to travel through all the cables leading up to a node before reaching the node itself. This problem is called a deadlocked feedback loop. If your composition has one, Vuo will tell you so and won’t allow your composition to run.
This composition is an example of a deadlocked feedback loop. Because the top Hold Value node could receive an event from the Fire on Start node through the cable from the bottom Hold Value node, the top Hold Value node needs to execute after the bottom one. But because the bottom Hold Value node could receive an event from the Fire on Start node through the cable from the top Hold Value node, the bottom Hold Value node needs to execute after the top one. Since each Hold Value node needs to execute after the other one, it’s impossible for an event to travel through the composition. To fix a deadlocked feedback loop, you need to remove some of the nodes or cables involved.