Accept defeat. Two simple words but they can hold incredible value. You need to accept that your opponent has played the match better than you, or that you made mistakes that led to your demise. This may sound harsh but it is way better to accept that you have lost than to get angry over the fact that you lost.
If you get angry over the sole fact that you lost than you focus all your attention at the sole fact that you lost. You limit yourself to focussing on the fact that you lost that you forget why you lost. You forget to think about the mistakes you may have made, and ultimately, you forget to learn from them.
But if you accept the fact that you will lose some games eventually, no matter how strong your deck is, then you will be able to focus on the important aspects of defeat. Because even the strongest decks have their weakness, even the strongest decks can be defeated by a weaker deck if the player of the weaker deck knows how to exploit the weakness of the stronger deck (see “Knowledge = power in any cardgame” for more about this).
So next time you suffer defeat, as much as it may hurt. Just let the suffering be and instead shift focus away from the pain of defeat and think about why you lost. In doing so you will confirm to yourself that the outcome of the match isn’t a guarantee and that your opponent may have played the match in a way that you never predicted or that you may have made some mistakes. If you can figure out even one thing that your opponent did well that gave him the victory or one thing that you did wrong that caused your defeat, it will hopefully give you some solace. Knowing that it is not the luck factor that determines victory or defeat, but the way the game is played (see “It’s not your last turn that determines win or loss” for more about this).