The rule isn't about violence. It's about the fact that someone who commits a wrong can't rely on the victim's prior diminished circumstances to mitigate the impact of their own wrong.

The person who smacks the eggshell-skulled victim upside the head with a magazine couldn't imagine that doing so would have fractured their skull. People don't normally have skulls as thin as eggshells. "Tough shit", says the law. "If you don't want to expose yourself to the risk of fracturing someone's skull, don't hit people upside their heads with magazines."

By the same token, whatever frailties existed in Trib Corp's internal security, necessitating expensive post-breach cleanup, are justifiably imputed to Keys, not to Trib Corp.