Both examples point to the need of training. Buying various guns doesn't make you ready for SD in intense situations.
I recall a NTI FOF run where my partner came out and said that he 'shot' his son. Good guy targets get shot quite a bit at matches. I was 'shot' as a bystander by a SWAT certified officer in a FOF.
Thus one needs the training for a bit of stress innoculation.
However, if you don't have a gun at the ready - you definitely are the Petits. The shooting of a loved one is a failure to train and use sense in most cases.