For me: if everything is correct, rubbing the alum block on my face yields no burn or anything. If my lather is not good; slight burn. If my technique is not good; slight burn or worse. If my razor needs a touch-up; slight burn and gets worse depending upon how bad the razor needs the touch-up. Too much pressure: same thing- slight burn. Any combination of the above; BURN!

Keeps me honest and paying attention!