I think that threshold of loss various between gambler to gambler, it depends from his income ecc. About me, there isn't a threshold of loss, when I start to realize that I'm losing too much, I leave casino and go to have a walk, and will come to play in another day.
That should be.
When we are losing, just think of taking a break. It's hard to follow a certain threshold since there's always a temptation to pass our limits once we reached that point. Since we are ignoring what should just be the supposed bankroll on that day, then the best thing to do is to become responsible to stop.
Take a break then come back, later on, to see if luck is now on our side. Then if the same case happened, just repeat.