Suppose I have a circuit with voltage 4V and current 1A. By \$P=I~V\$ the total power across the circuit is 4W.
I have a \$20~\Omega\$ resistor and want to calculate the power loss over the resistor. By \$I^2 R\$ that is 20W.
This doesn't make sense to me. If the total power across the circuit is 4W, how can I lose 20W of power over the resistor. Where is my understanding wrong here?