Click on images to enlarge.
The rollover: "How often does somebody actually WONDER ABOUT ETYMOLOGY in my PRESENCE?? You GOTTA give me this!!"
The rollover: Kidding! Of course it means 'a statement with a one in ten chance of being true.' OR DOES IT???
The rollover: 'Prove the rule' actually comes from the idea that a king or queen had the legal right to punish criminal offenders -- thus coming down hard on 'exceptions' to the law was proving the power of their rulership. Either that or it's an obscure ELO lyric that became a proto-meme on Laugh-In.