This one has been alluded to in the past by other lists, but I think it needs to be more clearly stated:
The Torus Rule
Most RPG worlds are apparently torus shaped - how else can you explain why both the top of the world map wraps around to the bottom (and vice-versa), and the left side and the right side are also similiarly connected?
This is especially odd, since whenever the world is shown from above (FF6, Chrono Trigger, etc.), it appears spherical.
When Nobility & Peasants Meet
It doesn’t matter where the character came from… He’ll always meet the king, mostly early in the game.
It didn’t hurt
Your character can perform anything very well even if he’s got only 1 hp left. No pain, no hipotermia, no fatigue… nothing will get to him. But when you lose that last hp…
Time Control
Mostly, night falls only when you sleep.
The Optional/Hidden boss is always obscenely powerful and dangerous, much more so than the final villain. It’s a good thing for the world that these guys are content to stay hidden and have no interest in world conquest/destruction, because they’d probably pull it off.
The item (or whatever) you get for beating the optional boss won’t be worth the effort; all the powering up and such you did to make you able to beat the Hidden boss will make said item obsolete.
The male lead will always instinctively rush to the rescue of any imperiled female, even if he just met her, even if he just saw her and doesn’t even know her name yet.
Said unknown girl will have in her possession some innocuous looking trinket (usually a pendant necklace) that will somehow be of pivotal importance in saving the world later.
No matter how insignificant the initial mission/quest is, it is somehow the first step in a chain events that lead towards the hero(es) having to Save The World.
We Don’t Need Any Freaking Oxygen:
Ever noticed that the pcs don’t have to breathe? They can walk around on the moon or in underwater cities and be perfectly fine. Who cares if there’s no oxygen- they’ll be fine! [/b]
Part B: Of course, you can still cast fire spells underwater aswell!
Part C: …Those guys must either have one helluva heavy armor/lead boots to keep them walking under water and not float…
Yo Ho Ho And A Bottle Of Rum!
Unless they are said to be evil pirates. Pirates are always a source of wares and occasionally, a party member.
Finally, a law of physics is respected!
Small characters are fast. Big characters are slow. Big characters usually have rocket launchers, axes, or if they fight bare-handed, they’re wrestlers.
The Racist Projection
98% of all heroes are human. 98% of all villains are not human. Humanity hates non-humanity…
Bushism (a.k.a. the Shoot First, Ask Later Rule)
You never try to solve your conflicts with monsters by talking. Instead, you simply smash any moving thing that might appear in your way without a word. Exceptions are the uniques, but even so, only with a few of them.
They Don’t Know Who They’re Dealing With
Monsters will bully around and pick you for a fight in a random encounter even if you are 70 levels ahead of them.
Magic and Pants/Skirts Don’t Mix
Excepct for a few exceptions (Magus, FF6…), simply every mage you see dresses a robe.
Another Space Distortion Rule
No matter how much you run to flee from battle, you’ll always end up appearing in the same point where the random encounter monsters picked you.
Mass Invis
In more than half of the games, you don’t see the random encounter monsters approaching. They’ll only appear after they are close enough to hit you.