The main reason why people lose a lot of money in gambling because they play and play gambking even though they not know how it works. And in gambling you must know your limit so that you'll able to have earnings. Many people stays gamble and gamble eventhough they always lose because of greed in themselves.
Even if they know how it works, if they dont have self control they will lose money in gambling. I seen people in real life lost millions of pesos (in my country) in gambling and I have known a person who was requested by her son and daughter to be banned in the casinos near their area but in the end their mom still gamble in another area. No self control will result to bankrupt.