AC is a mechanical abstraction, it can mean anything from a blow glancing off at your armor, the enemy missing you, you dodgign your enemy, you parrying your enemy, or you simply toughing through the hit.

Now theres another thing that especialy third edition DnD players constantly rage at if its brought up: HP are also an abstraction. You dont actually get 20 fleshwounds before a kobolds tiny spear to the ankle finally kills you.
HP basically represent plot armor and grit.