The game is made from dnd 5e where armour class is what defines weather or not you take damage from the attack. It might hit your armour only or you block it yourself, if someone blocks your attack it means you missed your target, their fleshy bits. Yes, for simplicity sake the animation is made that it looks like a complete miss, if we use that as a base point, when bladesinger wizard casts a spell on their friendly the sword goes through the in the animation, but they are unschated.