After 8 hours of stump grinding, I’m knackered.  It isn’t hard.  The grinder does all the work, just sweeping back and forth, chewing up the wood.  It’s the low-level attention that wears a guy down.  At the end of each sweep, lower the wheel just a bit.  Take too big of a bite, and the wheel chatters, the machine bucks and the clutch starts squealing.