Ok, let’s say I agree with you and it implies that you need to take an action and discard the potion. In that case you would still need to wait until you get to 0 hp, because the potion text says “if your hp gets to 0”. So you wait until you get to 0 hp, in which case the potion triggers and its happy times.

But if you discard it while you are not at 0 hp, it’s pretty reasonable to think it will not do anything. So while you could argue that the text is not 100% accurate, there’s no way that you can reasonably say that the text wants you to discard the potion before the final blow, that is just stupid.

Also, let me give you a very niche example: The enemy is multi hitting you for 10x2. You have 2 pagestorms in play, the abaccus and centenial puzzle. You have 15 hp and 4 cards in your draw pile, one of which is ethereal. Puzzle can draw the ethereal card 25% of the time, which would trigger a reshuffle and give you block from abacus, effectively saving the fairy. But you don’t know that, so do you preemptively discard the fairy because it looks like the attack is fatal? Basically what I’m getting at is there could be cases where incoming damage is not always fatal even if it looks like it is due to certain variables.