Let’s say the following happens:
You log onto your freshly dinged level 80 Priest, and you find Culling of Stratholme as the daily heroic. “Great, let’s go there”, you think, and start inviting interested guildies to form a group. The group composition quickly reveals that you’re supposed to heal, even though you don’t feel strong enough for it yet. Oh well, you shrug it off and head in anyway.
Chromie gives you your “crate zapper” and you get to work. You quickly find 4 out of 5 crates, but the last one keeps eluding you and your party. After a good 5 minutes the last one is found, and the real fight can begin. Everyone buffs up and gets going. The trash mobs hit for an average amount of damage on the tank, and you’re doing your best to keep up. You know you’re low on Spell Power and MP5, but manage anyway. After two waves your mana is nearly depleted, and the fun begins. Somehow you manage to get through several more waves, and then completely run out of mana, with nothing left to do but watch the tank getting squished by an Abomination. The party wipes, and tries again. This time the mobs go down, and you face the first boss. Sufficiently prepared, you get through the boss without too much troubles, and he’s downed. Saved to instance. The trash mobs after that keep posing a problem, however, and after several more wipes and mana-less situations you give up and call in the cavalry.
You switch to your Paladin with Holy offspec, who is capable of healing every heroic in the game. Confident that it’ll go much better now, the party continues. You pull the first trash mob, everyone somehow gets massive damage, you can’t keep up and die. What the hell?! Second attempt, and everything goes smoothly now. After all the waves are done you wait at the “secret passage” for Arthas to show up, but the bastard is taking a LONG time. He eventually shows up, and you continue with no problems. Through the Gauntlet, all the way to the end, everyone rushes through, ’cause this has lasted long enough. The Infinite Corrupter is long-gone, but at least Mal’ganis hasn’t bored himself to death yet. And then the unforgettable words echo:
“Hey, where’s Arthas? Did anyone talk to him?”
Silence. You didn’t. By now the respawns have appeared, and you fight your way back to the start of the gauntlet, where you quickly speak to the soon-to-be-corrupted Prince. He runs off, nearly dies, but gets saved in the nick of time. You rush through the gauntlet for a second (or third?) time, start the Mal’ganis fight and quickly kill him. Badges are looted, as well as the daily quest item, no one cares about the gear anymore. Everyone teleports back to Dalaran, and you quickly log off to get some much needed therapy.