It's true that losing isn't fun, and whatever the reasons our side seems to be losing all the time seem quite outside of our control. That's hard no matter which faction you're in. But there is a thing we've all heard about growing up called "good sportsmanship." When we play competitive games with each other, the idea is that we're supposed to enjoy the actual playing of the game more than the winning or the losing. Indeed, as with anything in life, if you get too attached to the outcome of a particular endeavor, you are less likely to do well than one who plays for the love of the game itself.
I've been thinking about this lately because I myself don't want to log on to WoW only to feel like the game is like banging my head against the wall. It has helped a great deal to realize that whatever rewards we get are more like milestones along the path, not really an end in themselves. After all, if I play, it should be because I truly enjoy playing, not because I absolutely must posses some item that will be out of date in a few months no matter what I do. This realization has enabled me to pace myself, so that I don't allow long losing streaks to carry on for hours and ruin a good part of my day. If I'm losing a lot, I can stop and do other things, then come back to it another time with an entirely fresh set of allies and opponents -- and more importantly, a fresh desire to do my best and improve my skills. WoW is supposed to be fun; but if it isn't fun for you anymore -- whatever the reason -- then it's time to either change your approach or do something else.