Warriors out in the world don't have their armor on 100% of the time.
I'll give you that - but how often does something occur while bathing?
(I didn't add sleeping or bar fights because I'm giving those to you... bathing is the only one I can think of).
Bar fights, ambushes when at rest in camp or sleeping, training (scarred hands, accidental injuries), duels, general fights when at war (many weapons intended for more than one hand relied more on the ability to crush armor inwards rather than to hew straight through it; cuts and stabs and the like happen when there's a big enough rent to jam your smaller blade into), ambushes while tired while on sentry duty, traitors in the camp, house attacked by brigands or opposing faction, made enemies among the opposing faction by being too awesome at fighting so when they're around town there's an assassination attempt, rode in half plate for speed and was attacked, magical attack, out hunting and attacked by a bear...
There's no shortage of reasons or ways a guy is caught off guard without his armor. Five tour frontline vets with no injuries are lazy authors, not good swordsmen.
And, for that matter, I expect everyone who RPs to at least know the rudimentaries of what they're writing. Best if they're good at it IRL, but it's fine if they look it up on Wikipedia or something. Do a little research. I guess my biggest peeve is people who RP medics and don't know how to do medical stuff, I see that way too often.