Since 2.6.0, the Full Life condition can be met even while the player is taking damage over time, as long as the player is recovering more health than they are losing.
The Agnostic doesn't work like this. Even if the player has enough regen to out-sustain the damage over time they are taking, and every single other Full Life effect in the game would be active, The Agnostic will still drain 20% of their mana per second.
External link →The Agnositic is part of your life recovery, which is allowing you to out-recover the degen. In the case where you are on full life, the Agnostic will not drain more mana per second than the total amount of life being lost per second - the mana drain and matching life loss are lowered if it can counter the life loss at a lower value.
Similarly, if your mana is empty, it can only drain as much mana as you recover each second, and the life recovery is based on that value.
That is what I suspected at first, but it isn’t the case. I am playing an RF build that is fully capable of sustaining full life without The Agnostic, but I still lose the full 20% of my mana per second. I’m not home right now, but I can post a video soon.
To clarify, The Agnostic handles lowering the drain when total life lost per second is lower than 20% of your mana. It does not and cannot account for any other sources of life recovery that are also countering some of that life loss, only not countering more itself than there is. I.E if you are losing life equal to 10% of max mana per second, then Agnostic will only drain 10% mana per second, not 20%, because that's enough that it counters all the life loss. This calculation can only account for The Agnostic, and is independant of other sources of life recovery.
From a mechanical perspective, the Agnostic cannot possibly know whether your total life recovery is outpacing total life loss per second, because the value of total life recovery cannot be known until after The Agnostic has calculated how much life recovery it's providing - it's a part of that value, so inhernetly has to be an earlier step - so the more direct answer to the question in the OP title is "because the Agnostic has to have worked out how much life to apply before total recovery can be used to determine whether you count as on full life or not".
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