It isn't the resistance I marked. I marked the wire gauge and length. Wires make heat when they pass electricity. Too much current for the size of the wire and it gets WAY too hot. In theory the breakers protect you. In reality, the breakers are rated based on in wall wiring, your extension cord is an all bets off situation. A 20a breaker requires 12awg in the wall and will not know or adjust when you plug in a 20awg cheapass extension cord.

FYI, coiled extension cords are also a fire risk because they are an inductor in addition to a resistor and concentrate the heat in a smaller area.

Also FYI, the resistance of the wire increases with length so lower voltage in the device the more wire between the device and transformer. Smaller wire also has higher resistance and increases this effect.

TLDR, use the fattest wire, lower awg is bigger copper don't ask me why - euro sparkies use cross sectional area so bigger number is bigger copper over there, and shortest wire possible.

Plug in something that draws a few milliamp and it will never matter. A hairdryer or an electric kettle draw much more and are a real risk.

On my list of things everyone should know that no one knows. At least the basics from the TLDR and the coil thing anyway.