Share an experience of someone who has access to extensive training and still made a mistake. React to the notion that even people with significant experience can fail or make mistakes.
It's is probably more common than you realize having experience and still screwing up.  My ex was in the AF and his job was combat arms training and maintenance (CATM).  He was emptying out his gun one day, but got distracted.  He thought he had cleared his weapon and so he fired the gun pointing at the car.  The bullet ricocheted off the trunk and out the window in the direction of people standing outside.  One of his fellow CATM members once thought he had cleared his weapon and so pulled the trigger.  He was in his truck and I think he shot his radio.  You'd think an AF Cop would know how to drive, but one hit me on Elmendorf AFB causing $5k in damage.  Military can be very stupid too.