From any parent! I used to think this was simply a threat of punishment, made by the parent to the child when the child was misbehaving and apparently out of control in the evening, but I now see that is too simple. Small children have a habit of becoming hyperactive at the end of their day. They will rush around in a frenzied manner.Curiously I see the same in puppies, so it may be some mechanism to burn off excess fuel ! It commonly, if not invariably, ends with the tired child becoming weepy. It is this observation that led Nanny to make the statement to , and of,her charge, by way of saying that it was time the child was tucked into bed. So it was a prediction born of experience. It is now often used to describe what the speaker perceives as a 'childish' piece of behaviour, particularly by some politician, which will serve little purpose, produce little result and 'end in tears'.