When you enter the small room you see a skull with some jewels in its mouth on a stone block toward the back of the room surrounded by assorted treasures. You don't know that the skull is Acererak the demi-lich. You don't know his powers to suck the soul of the most powerful character in the group first. You don't know the unique combination of magic items and spells that can defeat the demi-lich.
You're also not sure how you made it this far and whether or not it was worth getting several characters killed along with numerous henchmen.
The most powerful member of your group walks up and picks up the skull...