think of the thickness of the insulator on top of mcpcb.
Now think of grabbing a sheet of that, and touching live mains with your finger the other side of that microns thin sheet.
You'd be hoping there was no rip or tear.
You'd be hoping that you didn't get at least a capacitive shock.........and if a 1KV line transient happened at the moment of your touch, you would get a significant tingle.
Ive touched the plastic outer case of 7/0.2mm wire containing live mains and got a capacitive shock from that.......this has happened to me regularly, as I work quickly,and don't take full precautions when I work with live mains. I am well used to the zap.....but if the zap happened at a 1KV transient, I might think it was more than a zap.