This idiom dates back to the 17th century, where pots and kettles were in the mainstream. Obviously, the saying has a hidden meaning-- so what is it? This one is dealing with hypocrites-- who say and do something wrong, but are constantly correcting others. Racism is at the forefront, calling someone out, because of their national-heritage-- although is a immigrant themselves. Or, condemning a person for committing crimes, thus does an illegal-action, as well. Class warfare is a biggie, the rich looking down on the poor-- however, being without any money, at a point in their lives. The list can go on and on-- the moral of the story-- we want "kitchen appliances" to get along.