Two miners both come back home from work in an elevator. One miner has soot all over his face, but the other has a clean face. The one with the clean face wipes it with a hankercheif. The other does nothing. Why?
Answer
The one with the dirty face looks over to the miner with the clean face and assumes his face is clean. The miner with the clean face looks over at the one with the dirty face and thinks his face is dirty too. Thus cleaning his face with a hankerchief.