Knowing when to stop is not actually about your losing side but could also be on our winning side. It is important on both sides for me. It limits your loss and it maximize your winnings. If you apply it on one side things will become unbalanced and might drive negative results.
Some people makes it hard to themselves when they don't have anything anymore and force to play more instead of making it their last attempt for their million dollars luck quest. That's why if you are one of those who stop themselves on playing and other source to make money and become successful with that, you want to tell others that there are lots of opportunity out there and some of that opportunity might fit and also for you.