Thomas Shey
Legend
One knows one's own Armor, and how often they should get hit, at least if one is proficient.,m
Look at how many iterations of that one would need to have occur to figure that with any reliability with a system as swingy as a D20 some time.
Likewise, the training rules aren't just a PC thing; they are there to limit PC growth, but they are done by NPCs, and the NPC has to figure out the relative skill to be able to teach the student the new material.
Every ability is testable.
There's nothing to suggest many opponents are even vaguely in situations to get what one would think of as training, and yet they still arrived at their skill somehow.