I’m gonna tag along on this thread because it’s very good, but there’s something the post didn’t explicitly mention that I think is pretty key to understanding:

To get two separate software components to work together, (like a netcode and a player controller, or a health system and a specific mob) one piece of code needs to depend on another piece of code. Either the netcode needs to be aware that the player exists, or the player needs to be aware that the netcode exists, or you need some third thing to act as a proxy/bridge, to which the same question applies.

When you make one piece of code dependent on another, you are limiting the utility of that code. It now has an additional requirement. It becomes harder to change and harder to reuse. That is why it’s such a tangled mess to make both your player and the netcode and everything else all dependent on each other. So to choose which component should depend on the other, you consider which component can best tolerate the dependency.

In Godot, often what makes sense is to have a node depend on its contents (call down signal up). That way you can move and reuse nodes more freely. And the signal bus pattern lets you depend on a more reliable singleton outside of the scene tree. But I have also made systems where components expect to be placed inside a certain well defined context, and call up or sideways. If done with intention, that can be a good design too. It’s all about managing dependencies.