Having 100% reduced effect of curses in Path of Exile means you completely negate the effects of any curse applied to you. However, there are some important nuances to keep in mind:
What it means:
You will not experience any negative effects from curses like reduced movement speed, increased damage taken, or reduced attack speed.
You will still be considered "cursed" for certain mechanics, such as Coward's Legacy's self-damage mitigation.
Any "increased effect of curses on you" modifiers will counteract your 100% reduction, potentially applying some curse effects.
How to achieve 100% reduced effect:
Passive skills: Several ascendancy classes and skill trees offer passive bonuses to reduced curse effect.
Gear: Certain uniques and rare items have modifiers that reduce curse effect.
Jewels: Jewels with specific mods or anoints can significantly contribute to your curse reduction.
Flasks: Curse removal flasks like Witchfire Brew or Cinderswallow Urn can provide temporary immunity.
Pantheon: Specific Pantheon powers offer curse reduction or immunity.
Important points:
Remember, reduced curse effect is additive, not multiplicative. So, having two sources of 50% reduced curse effect will result in 75% reduction, not 100%.
Having 100% reduced curse effect can be very powerful, but it might not be necessary or the most efficient use of your resources depending on your build and content.
Consider investing in other defensive options if you find curses aren't a major threat.