Well, not "complete" nonsense. It's true sometimes. We don't get to hear the barbarians' version of Roman conquests, for example, because the Romans could write and the barbarians couldn't.

But that was a while back. And modern archaeology and critical historiography have done their best to balance the picture.

(Another good counterexample to the proverb is that the Christian version of the Crusades really was written by the losers. And I've even heard that are there English accounts of the American Revolution.)