If using a screw to bolt something down or just screw driver slipping and hitting existing wires. Im an electrician by trade I have seen a million different accidents that have occured from accidental stupidity I call it. Drilling through something without checking the other side is a common one. I drive a car that the electrical system is sensitive and shop labor is expensive so I take precautions as much as I can. Ever see a tech take an airbag to the head while working on a dash I have not only does it **** for the poor bastard that got hit but its an expensive screw up. And for all that ay they never have screwed up you either dont do anything or just havent been doing it long enough.