If i put my foot exposed to ground and put my finger to the USB power, i will be electrocuted. So the electron(s) from the USB power is passing over my hand, run to foot and go to ground ? As i might thinking, so ground must be an object that can pull excess electron toward them and the pulled electron will spread out to the ground or go to somewhere that more positive, so that reaction can continues forever (if i put a LED light with one terminal to power and one terminal go to ground it will emit continuously). With this argued, i think the ground or wall must be conductive. But ironically, the truth is not as i expected. Can someone please explain for me what happened inside these reaction ?