FAR too many DPS players think that their job is to do so much damage that they shift phases when their group isn't ready, pull off their tank, and attack anything and everything despite how the enemies are marked.

The tank doesn't get to decide to only tank one of the three enemies just because it's far easier for him to continue living with only one beating on him.
The healer doesn't get to ignore the rest of the group just because it's easier for them to focus on the tank.

Dps doesn't get to just spam as much damage as possible because that's the easiest(and most epeen-flexing) way to play.

Everyone is supposed to work together and that includes the dps.