User blog comment:Masterzach32/Item discussion - Black Cleaver/@comment-12314620-20140430203231

This blog is severely outdated. This was an issue in pre s3 when black cleaver got minor overhaul and the armor reduction was actually stacking.

Also on side note "don't focus tank" is practically another bronze myth. Your focus depends very heavily on your champion and enemy teams positioning and so, in many cases focusing a tank is actually the best decision.