Another counter example is when the thing you are recording literally _is_ the natural key. Phone numbers are a good example of this. There is no situation in w

Another counter example is when the thing you are recording literally _is_ the natural key. Phone numbers are a good example of this. There is no situation in which some data entry error will break a number. That is the creation of a new distinct (possibly) broken number. A phone number doesn't care about any externality in the world. It is what it is.