No this isn't about fuzzy logic, as cool as that is. It is about fuzzy rules and the way OD&D works out of the box. Because many of the folks playing the game in the first few years, including myself, had a background in wargaming and chess? Lots of the distinctions made in those early rules were accepted without much comment by participants. Pawns move one space, knights can hop over other pieces, a queen can move any direction the player wishes ... that's the way the game worked. Sure, in real life a common footman can go any distance on the battle field he wishes (within the limits of his capability) and a queen would rarely if ever be seen on the field of combat but that isn't how they work in chess.
Similarly, magic-users in OD&D and its immediate successors were not able to wear armor. It never said why in those rulebooks, it just said they couldn't do it. Clerics couldn't use edged or piercing weapons, fighters had no ability to cast spells, and when they were introduced to the game a short time later the thief class could only use leather armor. No explanation was given for these limitations, they were simply listed.
As I recall it? My Shattered Lands campaign ran for years before anyone ever questioned why a magic-user couldn't wear armor or carry a sword. As an aside, how many referees heard "but ... GANDALF was able use a sword!" during that discussion? Thinking I would head off any future arguments about the issue I optimistically put reasoning into my house rules as to why certain things worked the way they did. This only spurred even more vehement arguments about how properly fitted armor wouldn't inhibit a spell-caster's somatic spell components, or how my cleric would not wish to only spill blood in the rituals dedicated to his deity, etc.
See ... giving an explanation indicates you are trying to justify the rule. In reality, however, many of those rule restrictions are there for game balance and not necessarily how the historical or legendary basis for that class worked. I've covered before but it bears repeating as an example: the magic-user's ability to cause mass damage or bend reality is balanced by how thin-skinned he is in combat. One may further assume clerics were not granted access to certain weapons because magical swords were among the most powerful melee weapons in the game. A cleric wielding a holy avenger would usurp the fighter's niche as the preeminent fighting class.
All of this is pure conjecture, by the way. Logically, it fits but that doesn't make it the truth. I've no special insight into the minds of the game's co-creators and play-testers.
At any rate? Rather than trying to justify why a player-character can't do "x" or use "y"? Simply tell them they can't and move on. Trying to explain it simply opens the ruling up for debate. If a player stubbornly refuses to yield on the point and presses the debate? Perhaps the referee should gently suggest to the player that he may conceivably be happier playing a different game (or at least in a different campaign). While there is nothing wrong with debate, do you really wish to spend
valuable gaming time in a non-resolvable argument concerning whether a magic-user can wear plate and carry a longbow or do
you want to kill some goblins? I know how I want to spend my gaming