Go do the RDM job quests. Something along the lines of if your don't maintain the balance of Black/White Mana, you become Mana Starved or something and become like a Vampire, needing to feed on the aether of others. As WoL we don't succumb to that because of plot armor, instead...if our Black/White mana are imbalanced by more than 30 (i think), we generate 50% less mana in whichever color we have less of until the balance is corrected (and as shown by the crystal in our job gauge changing from Red (correct and near balanced) to Blue (imbalanced).