Illustrations of Sassanid Persian Clibanarii

[Urselius]

And Henri II of France was killed by a lance when wearing the best quality plate armour, reinforced for the joust. There are always incidents that can be quoted to support virtually any argument. The Byzantinist Birkenmeier made an analysis of wounds caused in cavalry versus cavalry battle, as described in the 11-12th century combats in the Alexiad. Though lance combat lasted a short time - lances were shattered or discarded for melee weapons quite quickly in battle - lances caused 32.1% of serious wounds and lances were the largest single cause of serious wounds to the torso. 87% of lance wounds resulted in the victim being unable to continue fighting.
These combatants would have had shields and I maintain that the shield was the mail-clad horseman's best defence against the lance.