There are gamblers who have that good discipline which allow then to prevent making big mistakes and incorrect decision making, those who understand that gambling is mostly for fun and not a venue to quickly win money, like what you've said if you have that mindset that you will use spare money or allocated budget which you can afford to lose then after losing the amount you are free to quit and stop, but not many have that same thinking and most are unwilling to accept defeats and keep trying to recover what they've lost.
I don’t think there’s any point in trying to win back what you’ve previously lost. Of course it’s a good idea to keep track of your stats so you can see the total amount of money you’ve spent on gambling and how much you’ve won from it. That way you can see the overall numbers, whether you’re in loss or, if you’re a good player, what kind of profit you’ve made. This overall statistic is important to understand how profitable or unprofitable gambling is for you. But under no circumstances should you chase losses because that changes a player’s psychology and can easily trap them.