I think that this has happened to all of us at some point, I've seen some friends who have spent a lot of money in physical casinos, it has happened to me in online casinos and the fault has been because I have not been able to contain my emotions, one says that one can control one's emotions, but it is difficult to be playing and controlling that game without losing control, that is the difficult part, it's easy to say it here, what I think when I play is that the money that I am going to spend will not be recovered so quickly since it requires a lot of effort, that is what can hold me back sometimes.
Usually while gambling we should expect the unexpected from gambling and anything could happen. The most important while gambling should be that whatever amount we are using to gamble should be the amount that would never be that effective to us when lose, became most people so much focused on using amount that are big so that they would also win something very big as well, but it doesn't work that way. Any one who understood how the gambling works would never be that angry whenever they loses their money while gambling and of course people are so much focused on the winning that is involved while gambling.
You're right, since it involves betting on something or an event that's yet to happen and can't tell what the outcome maybe, it's best to gamble with something that won't be effective to us open lose like you've said, in a lay man's term it's simply something one can afford to lose, it's very risky to bet with all the income we make hoping to double it through gambling those are the very steps that leads to pursuing loses and furthermore, addiction.
People should understand that they can't win everytime no matter how careful or strategic one claims to be you'll definitely come across loses sometimes it comes in streaks and when a gambler notice that they're losing too often it's best to pause and try again some other time.