The purpose of playing a game is to have fun. In a multiplayer game, i have never purposely quit a match. Sure, there have been many matches where my teams were more than likely pet monkeys who had been handed a controller, or the enemy team have been a group of elitists and the rest of my team have left in tears, or that it just so happens their overall kill score is 15 kills higher than ours and still rapidly rising.
If i am having no fun pursueing the current objective, such as "working with my team to get more kills than the enemy in 10 minutes", then i change objective in an attempt to have more fun. So on Halo, there is that level Sand-trap, you know the one, massive desert, two large structures with a narrow and deadly bit running inbetween them? the one with 2 of those massive vehicles that are pretty much completely useless when you are driving them?
me (and my friend, whom i usually play co-op with) will often change our objective to "lets try get both of these babies into that big deadly stretch of land!"... why? i don't know... but everyone else seems to have more fun when we do that.
Our team soon latch onto the idea like a sex-deprived rabbit would a furry hand puppet and an an entirely different battle ensues. our enemy are suddenly baffled by why the enemy team completely ignore them, running straight for that big-useless vehicle in the distance and driving it slowly toward that ridiculous destination! and then one of them catches on, and after ensuring our team is respawning somewhere on the other side of the map, will get into the vehicle and drive it further AWAY from that strip of sand...
Its oddly enough, a magnificently entertaining game... plus, you'll find that the amount of Kills for both teams spurts up in turn at about an equal rate.
That or me and my friend will play "Cat and suicidal betrayed mouse", a game where we take turns running into the open, spraying some bullets randomly at a nearby enemy and retreating into a building... doing this again and again will eventually force even the most patient of people to just run in after you. just around the corner, the other guy will be there, and he will stick me with as many stickies as he can... i then run back around the corner toward my pursuer's and get a brilliant reaction everytime... i can more than guarentee you will get severalpeople who panic and run backwards, sticking you with more grenades as if it will somehow resolve the problem...
another thing i love doing is laying down a trip-mine underneath a parker vehicle so it is as hidden as possible... funny when 5 minutes later you get a "triple kill" or something as you have just respawned ;p
I hold a great respect for players who continue to play through a match, no matter how dick-headed their team was, no matter how beaten they are, and just stick to it til the end. I encourage my team to collect and conserve bubble shields, so we can throw him/her a "bubble party" ^^