I agree with you on the second paragraph of your definition of money you can't afford to lose but not particularly on people that has a job, once you have gone way above what you can't bear in mind when you lose it or likely feel fearful of losing such an amount of money, it doesn't matter whether you are working or not, whichever way you get the money dash or through job, take you for instance, that someone dash you money, let's say $20, you will be at peace losing $1 than losing $5-$10 out of it regardless.
The gambler who had their job can able to afford the loss,kindly consider the gamblers who doing gambling with all the money he received from the small part time jobs.Already his condition was worst because of the low income due to the part time job,the gamblers who doesn’t able to accept the loss should stop playing when they start to face the loss in the gambling site.Mostly the income generating gamblers will use their income to the gambling site for the rotations of their gambling betting.