I think it was supposed to be a "rule of thumb" not a law of nature. I heard it used in response to "snake oil" cures that were supposed to be completely harmless but cure everything from cancer to pancreatitis.
If you carry it out to the point of absurdity, even water can kill people if too much is ingested too fast.
If you carry it out to the point of absurdity, even water can kill people if too much is ingested too fast.