Is this true? Why should I believe it? Certainly unclear to my sub-average brain why it's a "mathematical definition." I'd call it an empirical fact, but has anyone bothered to measure? Logically speaking, the curve's hump could be biased one direction or the other, or bi-modal, or whatever else...
Also unclear to me why it follows that "top of the curve" people can't explain things to their lessors. Sure some may not possess that skill, but you're telling me there aren't good teachers/tutorials out there? My brain's too soft, so pack it up? Seems presumptious.
Anyway the message of "know yourself and your limitations" is fine and well.
PS. Thanks for noticing I'm a tad above average, statistically speaking!