Some people call this retard checks.

Its a dungeon mechanic, much like a boss gear check in the form of "kill the nail before it explodes and kills everyone" and if you don't have a group with good enough gear you wont be able to kill it fast enough.

Only this is a retard check. Meaning "can your group members watch a youtube video prior to running the instance" or "can your teammates see the debuff counting down that kills you and make it to a very obvious location to remove it"

Its usually a mechanic to make sure your group isn't utterly brain dead...which is why they call it a retard check.

"don't stand in the stuff that kills you" Well if they made that just give a slap on the wrist for failing to do so...then why bother even moving...right?