Affects the amount of damage dealt by both physical and magic attacks, as well as the amount of HP restored by healing spells.
Because Determination has a lower coefficient than either Direct Hit Rate or Critical Hit, it is generally considered the weakest of the three DPS substats.
Determination is somewhat more consistent as its effect is always active, and it is slightly more flexible than Direct Hit Rate as Determination also improves healing.
While the in-game tooltip specifies that determination only affect healing spells (i.e. global cooldown actions), it also boosts the healing from abilities (i.e., off-global cooldown actions).