Talk:Shen/@comment-12049719-20131212111836/@comment-8506165-20140118040245

"thornmail and randuin have negative scaling with each other. enemy takes damage when he hits you. enemy hits slower when he hits you.

???? just why"

Thornmail is more to reduce the effectiveness of lifesteal by massively reducing the physical damage you take and damaging the enemy in return rather than being an all-out offensive choice, although as an AA-dependent champ it's quite difficult to duel someone sporting a Thornmail.

Randuin's is the more generalised anti-physical damage item, granting the highest amount of effective physical health of any single item in the game with the AA passive and slowing active just being gravy.

They serve different purposes. If you're trying to splitpush but they've got someone who can duel you through healing more in lifesteal than you can deal (thus making your effective health irrelevant because you can't damage them but they can damage you) then Thornmail becomes an excellent choice. Or if they have multiple AA-dependent champs and you vastly reduce their teamfight potential by making several of their team members take damage whenever they attack you - in a game I was in against a team where they'd been stupid and made their comp Aatrox jungle and Wukong top and obviously an ADC, two Thornmails on our team made it impossible for them to win any teamfights, even though they were more fed overall. Randuin's is just "I want to be tanky vs physical damage dealers".

Getting both isn't a bad idea if the situation warrants it. Randuin's is far less situational though because it's rare there'll be a game you don't want to be tanky vs. general physical damage and it improves your initiation/sticking power as a previous poster mentioned. The anti-synergy is somewhat true but in the situations where you actually need Thornmail, it really doesn't matter.