I feel like you're trying to conflate the gambler's fund with their potential wins. When we say "only gamble what you can afford to lose", we are talking about the gambler's funds and not the potential win they can get from those funds when they gamble. The whole point of saying "only gamble you can afford to lose" is to use your money where you won't suffer financially. Potential wins when you are gambling are not your money, so you should never think of them as "money you can't afford to lose".