meh even if you somehow have manashield up and running, not in cooldown, and not still casting when hit, as soon as the mana is gone, all the mages survival skills like the knockback of fireblast or group heals, a buff or two, even weakness (i use weakness often when walk-back-rushing to gurg...) are GONE. and when the shiled drops, you are still spamming mana pots instead of health pots...