>A similar things happened to me many years ago at a conference. The late Marcia Akins was talking about WMI and the uses of it. She showed how you could use it to list all the running programs, but she never understood why the list always showed one more application during the presentation than when she ran it in the IDE. I said that maybe it was the program she used to show the list which also listed itself. She slapped herself on her forehead and gave me a big thank you. I mentioned it to her later, how great the feeling of getting a nice attention from one of the real gurus was.

That's what distinguishes gurus from mere teachers: they don't need to prove that they know everything, they are great enough to publicly say they don't. And they appreciate learning from their students, and appreciate those students from whom they can get some valuable insight. Compare that with the run-of-the-mill presenters who don't like questions and even less like if you notice something they didn't.