Then there was the guy nailing up siding, examining each nail and tossing every other one over his shoulder.
 
Boss asks "why are you throwing away half the nails?" Reply: "They're defective. The point's on the wrong end."
 
Boss: "You idiot. You don't throw those away, you save them for the other side of the house!"
 
A quote somebody made was so good I saved it. Goes like this:
"Today's production equipment is IT-based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio."
 
IOW, it's not only about understanding your tools, but also the materials.