The old one:
The examiner is asking himself this question: "if this punter's next flight is with my kids as passengers, am I going to be happy?"
Answer "yes" and you pass, although you will get a bollocking for your various mistakes.
Answer "no" and you fail, even if the examiner has to be creative to find legitimate reasons for failing you.
That's the urban legend, anyway ... and I've never heard an examiner deny it. (Bet I will now though!)