Documentation
It is extremly hard, imo, to write documentation for something when you totally understand it (because you wrote it) and the person reading the documentation is clueless. I never cease to be amazed at the questions people will ask.

I truely admire people that write user documentation for the masses. Maybe that is one reason for customer support. "Nope... I'm not answering every stupid question in the doc. Let them call someone and ask."

Sigh...