Knights could wage war with relative impunity

Burdensome though mail, helm and shield may have been, they rendered William and his peers virtually invulnerable. Most sword and arrow strikes could not penetrate through these layers of defence, though lethal blows to the face and eyes were possible, and broken bones (especially from crushing lance attacks) were more common. Only crossbow bolts had the puncturing force to pierce mail and the padding below to reach flesh, and this helps to explain why the papacy sought to ban their use against Christians from 1139 onwards. In the majority of settings, however knights could wage war with relative impunity, and for fully equipped members of this warrior class death in battle was a relatively rare, even shocking, occurrence, 

T. Asbridge, The greatest knight: the remarkable life of William Marshal, the power behind five English thrones (2015), 51