I only stop when I have reached my limit for the day and regardless of wether I'm winning or losing, I try to put a stop to it at least for that day so as not to get myself involved in excessive gambling that will end up talking up all the ones I've already won. Being a superstitious gambler or waiting till you've lost for a certain number of consecutive times would likely make you loose more before you eventually stops either temporarily or for a long time.

Emotion at the time of gambling also plays it own role to keep one all glued to gambling regardless of your plan regarding your point of no return. It's just your ability to manage your emotion when it comes hard on you that will help you manage how vulnerable you are to continuous gambling without control.