And it is impossible to get back what he lost.
It is not totally lost. There is some possibility of winning big enough of an amount that you get back everything you have lost. But the odds are too slim. Still it is possible hence why people continue to hope on this little hope available.
And I think that even gambling addicts know very well that they have lost their money in the game forever. But some inner feeling, maybe resentment or hope to win and recoup still makes such a player continue to play. And accordingly, he continues to spend even more money.
Humans are naturally hopeful lol. Even when the possibilities are so little, there is always some hope deep in us that things will work out for the best and we get what we are actually wishing for.