Two firemen go into the forest to put out a small fire.
Afterwards, when they emerge and go over to the stream, the face of one is all smeared with black while the other man’s face is completely clean.
Which of the two will wash its face?
The one with the dirty face will look at the other man and assume that he looks like him. And the man with the clean face will see his colleague covered in grim and say to himself: Im dirty too, I’d better have a wash!!