There are many things I teach easily. I can teach a complete knucklehead how to cook a good meal.I can teach linear algebra to a chimpanzee. I can not teach climbing from scratch to a certified mensa member given three days and a powerpoint presentation.
For some reason, it takes me forever to teach the blake's hitch, anchor hitch, figure 8, and body thrusting to someone brand new to climbing. If a person already has a basic knowledge of those techniques, I can show them a whole crap load of new techniques in a single afternoon....heck in a single hour....and they retain it.
For this reason, I've given up teaching someone who has never been in a saddle. I don't do tree work full time anymore, only as a sideline gig and heck, I do all the climbing on the job site anyway, I just want my groundie to be able to do a rescue if I need it. I hope to work for myself full time with in the next year....probably this spring, but until then, I'll just keep paying a premium for folks who already know a little climbing rather than try to teach someone from scratch.