Comment by Koshkin
> we imagine injecting 1 amp of current into a single node
I have always had a problem with statements like this. Current is a (measurable) property of an edge, not a node (vertex). One can’t “inject” current into “a single node."
By definition, an edge connects two nodes. So clearly, "inject current into a node" is just shorthand for "inject current along a (real or hypothetical) edge leading to a node". This is very common terminology in electronics.