Why do we say “It is what it is”?

Philosophers used these words for centuries to say a thing has its own true nature. In 1690 John Locke wrote that everything has a real makeup “whereby it is what it is.” The shrug-and-move-on sense is much newer. An early example turns up in a 1949 newspaper column by J. E. Lawrence: “It is what it is, without apology.”