When you choose to play hardcore, you choose the thrill and excitement of death at any moment. You also choose the slow grind to get level advantage over bosses. You choose being able to say that you've played this game without dying. You also choose to be considered stupid among your friends, admirably stupid.
Well, it is all fun and games until someone dies.
In contrary to what you might believe it is not mobs of Sancturary that are your greatest peril. Not even the bosses. You prepare for those and you won't go into the fight until you're certain of winning.
You're greatest enemy is lag. When your connection to the server starts to lag and you don't know what you're hitting, this is when hardcore stops being fun and starts being about survival - because when network connection starts to stutter, you can end up either dead or alive with no real control over the outcome.
Another happy moment is when you resume your game, and is spawned right into a rare or unique monster you weren't ready for. He's been hitting at you for 2-3 seconds while your computer where loading up all the textures and your health globe is already down 50%.
When life or death is beyond your control, hardcore mode really sucks.