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So, here putting out the same question, what will make you quit gambling forever? A win or a loss, or both?
Neither of the choices you mentioned.
Choosing one means you're going to be addicted, why? Well it's very simple. If you win, you're going to be greedy, full of yourself thinking you could win again, much bigger, but in the reality, you'll experience the opposite, while if you loss, you're going to chase your losses. You're going to let your emotions dictate you on what you should do next, and the result would be chaos.
In short, the only reason that will make you quit gambling is by not trying it in the first place.
So in summary. It’s a decision and a choice that’s solely dependent on the individual and their approach towards gambling. Gambling affects different people in different ways regarding their attitude towards it. How and addicted gambler sees this is completely different from how a responsible gambler does. A loss can make a responsible gambler to quit gambling forever and so can a win. While also having quite the opposite reaction on an addicted gambler, rather than making him to think of quitting, it could serve as some sort of motivation to keep pushing harder until he finally reaches his breaking point. Sometimes it could also be vis ver sa too, depending on the situation.