I've seen a lot of posts lately complaining about tanks and a lot of people complaining about penetration. normally i wouldnt care but i just came to a conclusion.
after building somewhere between 300 and 400 armor... i was still taking 3k damage from twitch.
Crett3 votesThis is a VERY damage heavy meta, and as it is there are few ways to counter it. Sure, tanks shouldn't be facerolling entire teams through sheer durability, but as it is I think it's a little unethical how quickly they melt. Especially when it comes to % health damage
Armor doesn't do nothing, but it really does stop being very effective once they've got any kind of armor pen
When you buy 
you're looking at about... 43 effective armor from it
BLACK REALM GOD1 votesmy build was
edit while i realize that i didnt buy armor+hp items i checked to make sure and twitch wasnt doing true damage to me. just physical.
edit 2 and i know that twitch does a lot of critical. 
is the only item that blocks that but at that point %max hp damage would just take over and kill me faster.
ModWulf Helhammer2 votesTwitch's poison is true (small amount as that is).
Also you found the problem yourself: you have like no health in that build. All the armor in the world doesn't do squat unless you have health to back it up
BLACK REALM GOD2 votesAnd yet like magic 3k health was I'm my health bar. HUH weird.
adding another 1k of hp would have done 3 things. Gave me more regen (possibly by using warmogs) or through two 500 hp items, allowed me to get other items that have different passives which cost more, and regardless of the outcome twitch does 400 damage to me with his bork active and 240 which declines with the passive and that damage is only slightly modified by my armor thanks to youmuus and an additional 200is for his lord dominiks. So... Yeah hp wouldn't have helped.
ModWulf Helhammer2 votesAll the armor in the world doesn't do anything unless you have HP. Armor doesn't give you a shield or something, it just increases your effective Hp by a percentage of how much health you have. So when that number is low, you're not getting nearly as much benefit as if you had a lot more health
BLACK REALM GOD1 votesbut if you do the math - 3k hp (most players have around 2-2.5k hp at 30 minutes only the tanks will go for 3-4k+ hp. if i had more damage i could have just 1 shotted twitch. armor is pointless. when a champion builds youmuus and bork together you're better off just buying lifesteal attack speed damage cooldown - pretty much anything other than hp and armor because those two items when used together make it possible for an enemy to do more damage and live longer. it's gold wasted. building damage would have been better because twitch didnt have any armor and if i keep my life lower than a certain point he wouldnt have been able to lifesteal as effectively. he didnt have a lot of lifesteal after all. just blade of the ruined king.
Ruin Lance1 votesyes, there is no point in building armor because instead of dying in 4 seconds you will die in 0.1 seconds
dunkeroni1 votes
You now have have 300 bonus armor and crits only do 40% damage, which is all of Twitch's attacks.
BLACK REALM GOD1 votesi didnt buy that because of . those passives grant scaling physical damage and lifesteal based on max hp. i wanted to, but i was hoping tabi would do the same.
BLACK REALM GOD1 votesalso i was playing support so gold was hard to come by. especially with a sol for bottom :/
Dasdi961 votesIf you really want to be tanky, you should focus on health, and not resists. This is because it shields you from both types of damage as well as true damage like red buff and elder drake buff.
BLACK REALM GOD1 votesi wasnt trying to be the tank. i wasnt the tank. i was some goofy support in a weird composition that arrived out of a draft selection argument when a premade decided they were going to start a fight with their team for no reason. was just trying to do my best to stay alive and win. it didnt happen. regardless of all of that - it doesnt change the numbers. i get that armor works hand in hand with health.
is a website i just found that gives out most math equations involving league of legends. i think they're mostly right even though the site hasnt been updated in almost 2 years. when you add in the numbers for blade of the ruined king lord dominiks and youmuus (not including masteries and runes) it's just impossible to find a solution other than kill or be killed. all of those on hit effects happen 3 times every shot. not to mention twitchs ultimate which lets him do it to enemies standing in a line multiple times per shot.