short circuits can happen due to various problems . maybe you stripped the wire too long and it's touching something , maybe you did'nt twist the wire nut tight enough and it touches the wrong wire , maybe there's a break in the insulation . there's alot of maybes . a ground acts as a means to trip the breaker . in years past it wasn't used . now don't get me wrong , there is alot of stuff in the NEC that is just down right ridiculous but this is one of the things to pay attention to . i know that i really don't want to be the path to ground if the circuit decides to blow . sorry, i'm only a second year apprentice in commercial/ residential wiring but i get my info from my fiance'(22 years of experience) and his father(40 years of experience) in the trade . i have nothing against "getting the job done" but i guess if you do it for a living , you get a little picky !
