I periodically see discussions of players sleeping in armour. Or walking around a village in plate and mail carrying a battleaxe. There should be personal and social repercussions for this behaviour. No town wants to see strange warriors walking around (especially if they're better armed than the guard, yeomanry, or especially the local knight or lord). And I think sleeping in plate armour would be pretty uncomfortable.
The problem is, standard D&D is set up to heavily encourage players to do this. Billy the Baker's Boy, known troublemaker in the town (and a 0-level human), needs a 17 to hit Merk the Merciless, travelling adventurer (and 4th level Fighter) when Merk is wearing plate and carrying a shield. Take away the plate and shield, and Billy now needs a 10 or better to hit Merk, more than a 300% increase in hit rate.
The problem here is obvious. For his own safety, Merk pretty much has to be wearing that suit all the time. It makes such a big difference that it's likely to be a matter of life and death. Now, don't get me wrong, armour does make a huge difference to survivability. If it didn't, it wouldn't have been invented. But it's far from the only factor. The skill of the warrior and the weapon they're using to defend themself are far more important.
I've talked about the problem of not considering skill and weaponry on the defense before from the angle of verisimilitude. This is a great example of how faulty mechanics lead to bizarre behaviour. Let's see what the situation looks like if we take into account skill and weaponry.
Let's consider that Merk gets +1 to his defense for each level of Fighter - that's +4. Let's also consider that he gets +4 to his defense for carrying a sword (a reasonable weapon of self-defense, and likely to be allowed in many jurisdictions). Suddenly, our 0-level human needs a 17 to hit Merk, even though he's not wearing any armour!
Simply by taking into account skill and weaponry on the defense, we've eliminated (or minimized) one of the enduring and troublesome tropes of D&D. Now, I will admit to making these numbers up to match the original D&D example. I haven't finalized this system numerically yet. If anything, though, +4 underestimates the value of a sword by a lot.