Quote Originally Posted by Estellios View Post
PIE: Enfeebling Magic Potency and Magic Evasion. This is essentially your chance at landing secondary debuff effects (such as Aero's Damage over Time and Stone's Magic Evasion down) as well as your chance at resisting debuff effects.
PIE also increases your MP pool, which makes it important there, too. A nuker who runs out of MPs has to regen for a while before resuming killing the monster. A healer runs out of MPs and people die.