If someone lose his money in gambling because of have fun, he already consider that losing money is the amount he can afford. He doesn't mind losing that money for fun in gambling because he just want to enjoy his time in gambling and no need to feel sad if he lose.

That is the risk of playing gambling and he know that so he just use some money he can afford to playing gambling and walk away from gambling.

That is not stupidity or deceit because he calculate everything before he gambling. If he lose, he will not bother to recover his losses because he know that is what happen in gambling.