Quote Originally Posted by Slashley View Post
IThe boss already has -50% Atk from previous debuffs, doing 500 damage to you. You use a -10% Atk debuff. The boss now does 400 damage (100 less). You're taking 20% less damage from using a -10% debuff.
It's useful to conceptualize this as effective HP or # of hits that can be absorbed. Then the results exactly mirror the impact of DEF down on damage dealt. 100 less damage doesn't sound like much, but starting from 500 damage per hit, it increases your durability from 2 hits to 2.5 hits (25% increase). Add in the impact of healing and your durability could increase even further.