While you can gain many temporary bonuses in from completing different tasks, some of the buffs you earn are permanent for your character.
Each of these continuous boons offers something different, from stat increases to more skill points to spend on your build. Throughout each Act of the game, you have more chances to add more permanent bonuses to your character as they grow.
Not every permanent bonus will work for every build in , as every class has unique stats and abilities they want to prioritize.
Thankfully, most of the eternal buffs you can unlock are universal across multiple archetypes. However, some bonuses require you to make a choice, so sometimes you will have to choose one of two available buffs going forward in your playthrough.
One of the most common ways you'll earn permanent bonuses is to defeat different bosses in every story Act of the game.