u/Inevitable_Sir9871

Can someone explain why we don't consider the upper loop in first one? I'm totally confused.

Also, let's say in the second circuit I remove the 6Ω resistor. Why do we still consider the upper loop in that case? How does the supernode work then?

I'm having trouble understanding when a branch is considered "inside the supernode" and when it needs to be included in the KCL equation. Any simple explanation would be appreciated.

Thank you.