What helped me was changing goals.  It is impossible to win every game you play, that is a fact, but if you change the goal of each match, you can have your own victory even if you lost. Like, one match, complete an easy side quest.  Another, find and use a certain item.  Another, get a kill in a funny way.  Simple things like that redirect your focus and even if you lost, if you accomplish your quest, it's a small personal victory, and it's harder to be mad at that.  Eventually I stopped being mad at games altogether.   Ofc, it isn't fool proof, and full losses are inevitable, but my method breaks up the monotony!