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 doesnt same as lottery because if you compare let say dice game and lottery the chance to win in dice is far more higher than lottery because with martingale on dice you will still have a chance to win whatever your lost and with lottery this is pure luck game which is you never get back what you lost using martingale because what you aim is the jackpot so it will be harder