As the title itself, Im thinking about the valid reason why gamblers continue to gamble even if they are losing a lot of money.
Gambling isn't just about winning or losing money. Perhaps we find the happiness in gambling which won't be exciting for us, without putting our money at stake. I'm not a very profitable gambler but I'm decent gambler. I only gamble which I can afford to lose.
Then it might be your reason why you always come back to the gambling games. I am sure that there is any more reason for us to continue gambling because gambling is something that will tempt us to always come. But I agree with your saying that we need to gamble which we can afford to lose because we are not sad if we are losing the money.
A rational man will look at the reward before giving his time to anything. Gambling in a rational way is the real gambling.
You look at the output of the money you put in and the cost of your time you put in and calculate the benefits. If less, you do not go into the gambling and if high, you go into the gambling and enjoy it in the same time. There are people who are in gambling just for profit.