Increases the damage of primary skills by 25% multiplicatively. Primary skills are skills that do not cost Resource to cast and are normally rather weak in terms of damage output. They usually generate Resource. Wizard and Witch Doctor have Signature Spells like Poison Dart or Magic Missile that do not generate resource, they are considered primary skills hence buffed by this gem.
You can level this Gem all the way up to rank 150. Every upgrade will increase damage by 0.5% up to a maximum of 100% total. The rank 25 bonus grants 4% healing of your maximum health whenever you hit with a primary skill. It can only heal you once per cast even if you hit multiple enemies.
Simplicity’s Strength Best Use
The Generator Gem: Used in all damage dealing builds that rely and stack primary Skill multipliers like the Frenzy Barb or Zunimassa Poison Dart Witch Doctor.
Legendary Gem in Diablo 3
Legendary Gem Creation:
If you need extra Legendary Gems to level up, you can make the Rift Guardian in any Greater Rift drop a new Rank 0 Gem by removing all the Legendary Gems with the same name from your Equipment, Inventory and Stash.
The safest way to do that is to put them into the Inventory of different character.