Why do associates pass by out if they capture hit to complex??

I just dont achieve it.Why do associates pass by out if they capture hit to complex??
You watch too much TV...
It just happens within the movies...
Just like one shot and they spill out dead instantly...
Because their brain shakes inside their skull.
Its the body's protecting mecanizem, your body shuts down like a computer rebooting.
I don`t know blunt force trauma.