Good point, that's the very reason why you should only use the amount that you can spare to let go, as losing is unavoidable even how good you are, there's still chances that you may commit mistake in placing your bets, handling losses is tough as for sure most gambler do expect to win and earn money, while to those who knows how to balance their budget they can win sometimes and then lose after but the catch is they have winning side that they can share and a losing side that they can hide..
If losses alternate with wins, it's not that difficult. Things get harder when a losing streak starts. But when that's a rare occurrence, you don't even think about how to deal with losing, especially if you follow risk management and never bet more than you can afford. It's like with a disease, it's better to do prevention than to treat it, maybe it's not the best comparison, but the point is clear.