You can lose a lot of money with gambling, I lost around the 2 bitcoins with gambling on different gambling websites.
Of course this is logical you cannot always win but I still regret today that I invested so much for me in the online casino's.
Well you regret because you had losted but if you had won 4 btc with those 2 btc invested would you regret,for sure no,the thing is we cant win always ,its like play lotery,knowing that casinos has a better odds to win then lotery,but well in the end all had been made to be profitable otherwise wouldnt exist soo many casinos.
It depends per session. There are some moment that you will of course win some money. And that will be good. But if you win you should directly stop.
And some people are playing further and in the result they lost more money than they won and that is very bad.