You're Using AC Wrong
Okay this may be the nearest I have gotten to a clickbait headline, I don’t believe that Dungeons & Dragons are using armour checks wrong mechanically.
However I do think that a vast majority of us tend to role play them badly. I’ll explain what I mean and how we can get better.
When we are fighting in D&D 5e for the most part the battles consist of us rolling a d20, adding our modifiers and seeing if it beats the enemies AC before doing damage. Mechanically it is all quite straightforward, so don’t worry, I am not going to whack out some weird indexed rule that ruins the fun.
However often if, when rolling, we don’t beat the AC check, the DM will say you miss. And sometimes that just isn’t right. I guess it isn’t technically wrong, the DM is the storyteller of the collective adventure, but it isn’t always thematically or narratively compelling.
For example let's take a small party of two; Bob Axehand the barbarian and Sally Sharpshooter the ranger. First of all they are fighting a simple goblin. The goblin is unarmed and slippery. His DC is based exclusively on its dexterity. When Bob and Sally fail their hit rolls it is fair to say that this cheeky gobbo has dodged their blows. So the DM saying “you miss” fits perfectly narratively.
But say Bob and Sally come across a giant slumbering Ogre, after failing a hit roll, it seems wrong to say that the duo simply missed. Maybe this would make sense if they were blinded and thus had disadvantage, but in most circumstances our heroes wouldn’t be so inept as to not hit the giant massive target in front of them.
Bumbling large enemies, such as heavily armoured knights and other big beasts, are reliant on their armour for their armour checks, funny that. Thematically it makes sense to say that their armour has protected them from damage rather than their ability to dodge our attacks. For Bob we can say that he hasn’t swung his strength weapon with enough vigour and it bounces off the ogres surprisingly sturdy skin. In Sally’s case she might need to be more precise with her bow, its a dexterity weapon that needs to hit a weak spot in order to deal damage, it isn’t enough to hit but to hit where it hurts!
I understand that actually saying “you miss” is often just used as shorthand in a long fight, or it is used when we get a very bad roll, but keep this article in mind when you're DMing to keep things a bit more narratively compelling!