Fairly random question here: which fight can you simply not manage to survive, no matter what?

This is inspired by my experiences with Kael'thas. Now, of our four kills, despite the fact I've always been standing at the end, I have died once or twice in every kill we've made (4 ankh's, 1 soulstone, and today a battle res got thrown my way). We brought a number of new people along today and endured a couple of wipes when, on an attempt I ate a conflag-fireball without a mace buff and promptly fell over. I insta-ankh'd. As far as I was concerned, this meant the odds were good we were going to win. When, later in the encounter, I managed to pull a phoenix directly into myself as it spawned (hooray healing aggro) and fell over again, I was absolutely convinced we'd down Kael as soon as I heard the raid leader calling for a Druid to bring me back to life. It just had to be!

No doubt I don't need a shadow priest for Kael'thas because I use mana too fast. I need one to help me regen a little after each and every death.