User blog comment:ClariS/AD has Diminishing Returns!!/@comment-92.6.151.80-20120905093446

There is some seriousness to this, though.

Armor and Attack Damage both diminish the more you get, at least with respect to one another. Once your enemy has 200 armor, it takes A LOT of attack damage to noticebly increase your damage output.

Recent AP meta had already learned this, and this is why Abyssal Scepter was nerfed. Haunting Guise + Sorcerer's Boots + Abyssal Scepter reduces most non-tanks to below 0 magic resistence. And the formula for "damage reduction" is reverses and doubles when below 0. 30 magic resist is 23% damage reduction; -30 magic resist is 46% damage increase.