In your grandfather's defence, it is what pros do, as the pros rarely follow safety practices. It's so ingrained that I have to fight back to not start explain

In your grandfather's defence, it is what pros do, as the pros rarely follow safety practices. It's so ingrained that I have to fight back to not start explaining why getting zapped by mains is perfectly safe in the vast majority of cases. That is a piece of information that - while technically correct - completely misses the point that working with any risk whatsoever is pretty stupid when you can remove all risk by just disconnecting the circuit.