The maxim is always that you should only gamble with money what you can spare, but most people know that. More importantly, keep a bankroll for gambling, and a strategy. And under no circumstances go over your limits, try to put your emotions aside. Only then can you enjoy it.
Even if most people know that you should only gamble with money that you can afford to lose that does not mean that people actually follow the advice, after all it is very common that people are gambling and then they get upset because of a bad loss and instead of calling it a day and login out of their account they decide they want to keep gambling so they can recover that money and they go way over their daily limit and lose so much money that by then they have some problems paying their bills.