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As soon as that call goes out over Vent, it's over. You stand in the fire and die, or run into the eye beams, or make everyone annoyed because you do your best to survive when it would just be faster for you to take the death and run back in. And so you begin that trek back to try again, and the other familiar query is voiced:
"So, what happened?"
General replies fly back. The tank died. Too many DPS were down. No heals. Split DPS. Not taunted in time. DPS in the front. Standing in the fire/voids/ooze/blizzard/runes/poop.
Understanding what causes a wipe is paramount to raiding success. Learning from your failures is a cliche for a reason; it works. If you don't understand how or why you failed, you're doomed to a vicious cycle of repetition and repair bills, with little to show for it but what comes to you from sheer luck or stressed-out raid-mules (i.e. those who carry the rest of the raid).
Sometimes a wipe can be generalized. If too many DPS are dying because too many are standing in the eye beams, it may be as simple as saying "Yo. Stop standing in the dumb." If DPS is fighting in the front and your tank goes down because the boss has just ripped five new pretty bleeding holes from his skin in one second flat, it's obvious your DPS needs to take a cue from the hunter pets and grow a fondness for boss-monster haunch. And if you're pulling whelps, 50 DKP minus and stay away from the tail.
However, it's not always something you can simply generalize. For example, what does the phrase "the tank died" tell you? Absolutely nothing that the raid didn't already know. Of course the tank died, otherwise the boss wouldn't have pranced his happy self through the raid, smashing your healers as he pleased. Why did the tank die?
The first idea may be to blame the healers. After all, if a tank is dead, it must be because he didn't get enough heals. And, truly, this could be the problem. Your healers were possibly not ready for a huge influx of damage, there could have been confusion on healing assignments, they could have just not been ready, or they could have been dead. This is a little more complicated and requires a bit of a finer comb. Are the healing assignments inappropriate? Is someone trying to do more than they should and are stretching themselves thin? Have misunderstandings been cleared up about strategy? Are the healers in the correct position? Are the healers actually using their class and spec properly?
Perhaps it's not a healer problem. Maybe the offtank did not taunt in time, and your main tank's debuff became too high. He goes down in one hit and you're scrambling to catch up. Perhaps they missed something vital in their rotation, and they're suddenly taking more damage than they're supposed to be, at a time when healers are trying to boost up the raid in general. Does the offtank need to taunt pre-emptively? Does the tank need to go back to class and learn how to do a proper rotation? Does the boss need to be pulled out of, or into, some sort of glowwy fire contraption? Did no one warn the warrior not to charge Kologarn or he'll drop off the edge? Are they just not geared enough for the fight?
What about the DPS? Were they dragging eye beams through the raid? Did they not watch their threat? Was there someone with a gravity bomb who just decided it would be a good idea to stay in the raid? Did no one shatter the brittle golem? Were they all dead? Were they not grouped up tight enough so the meteor damage wasn't spread evenly? Did they not move when their charge changed? Was there no interrupt? Were they standing too close, and chained damage onto the tank?
Knowing why a wipe happens when it's something controllable is extremely important. It's the first step in fixing the problem. And there could be a myriad of little issues working together to create one big pile of corpses. Being able to identify the reasons past the generalizations is paramount. And, sometimes, pointing fingers is necessary, so long as it doesn't go overboard. If you don't point out that Rogueymcstabstab shouldn't be DPSing from the front in the fire with the candlestick, he's going to keep doing it. But calling him a weasel-faced toad-licker won't make him fix it, it'll just make him angry and more likely to pull threat and vanish.
Wiping, however, isn't always the fault of the raid. The boss could bug (a serious possibility in this brave new raiding world) and suddenly half the raid's eating dirt. You could get an unlucky chain of gravity bombs on your healers, and suddenly half of them are running out, unable to catch up for sudden damage spikes. A second too slow dodging an eye beam coupled with a sudden swipe of the hand through the raid and you have a dead player. Grobbulus could turn to infect someone in the DPS at the same time he summons slimes from the people in front of him and you have a legion of green snot balls AOEing their way through the raid, and the add tank is the one who's been infected. Or maybe your tank's just diconnected, along with a couple of your DPS and a healer. And perhaps Wintergrasp is going on during prime time and the server lag is so bad that your instant casts are taking two entire seconds.
Though those unlucky instances are not necessarily raid wipers, it is possible that, in combination with some other unfortunate deaths and circumstances (silences, mis-communications, unexpected damage, and so on) can greatly contribute. Most battles are no longer luck-based (like Prince in Karazhan used to be) but still can have "unlucky" elements. Controlling what you can will, however, help you recover from or prevent the bad luck, and hopefully down the boss.
Of course, if you don't, there's always the next time, right? And the next time, and the next time, and the next time...