When I first got my PPL I knew something the examiner didn't, something slightly obscure along the lines of whether or not the oil pressure gauge would continue work in the event of certain types of electrical failure.
He said it wasn't fair because I only had to learn the systems of one aircraft, whereas he had to know several and his day job involved having to have a vastly more detailed knowledge of a Herc (or Tristar or whatever it was) than he needed of a 152.