Simply means that losing is a normal part of the game. If you cannot accept losing, then you aren't ready yet to receive it and learn from it once it happens to you especially in a a losing streak. You may just deny it by blaming your luck or the casino just cheating on you. You gain experience by mastering yourself to control risk and not by how you win. Because winning is a probabilistic matter. So you need to remain liquid long enough to stay on the game.
Stronger people minimise their loss by accepting it and work for it while weak people always miss the chance by leaving their success due to a single defeat. If we have the ability to accept our win then we should also be able to accept our loss and then overcome those mistakes due to which we face such loss.
If you are going to be a part of gambling then you should also put in your mind that win and loss is not in your hand and the result of your gambling will totally depend on your luck therefore you should be mentally ready for both win and loss.
In life a person cannot win or lose continuously but there will be loss as well as win so don't be afraid of loss but work to reduce it while you win. Gambling is not a successful field so if someone accepts it even after knowing about its harmful effects then he should blame himself instead of his fate.