The feeling when you invest thousands of gold in armor then it just goes right in the trash BECAUSE someone only afforded a LW and he still manages to melt you like if u had absolutely no bonus armor.
Ah the wonderful feeling when your resistance doesn't mean shit against 35% pen!
Here's how it works:
Early game advantage: build armor while adc works on core items Mid game advantage: stack health so armor reduction doesn't hurt as much Late game advantage: build thornmail to screw over their lifesteal and armor pen
Actually it just means its less valuable compared to HP than it was previously, but still worth buying in the proper amount.
Offense out scaling defense is good for dynamic game play. A defensive slug fest reduces the value of plays and becomes boring.
Then you remember that (a) you bought the resistances for an early game advantage, and (b) you're supposed to CC that one guy what bought Last Whisper so he can't deal damage.
This guy have right (partly) draven late game BOTRK , LW , and 450 ad killed me in 5 SHOTS , i was olaf 350 armor and ofc thornmail , i was in shock and i am always when i think of it.
PS thornmaill was just preventing him to lifesteal allot BUT HE WAS STILL HEALING a bit. so he was full HP at end
The game needs %penetration in order to have some way of dealing with tanks. However, I believer the cost for the items are far too low considering what they do.
That's what people feel about 300 armor fh, thornmail and randuin's before they get lw.
even after lw you still tank a hefty bit of damage.
i dont buy defensive unless it comes with offensive stats ex 
