Law of limited invulnerability:
No matter how much damage you get, you will always be able to function at full capacity. It doesn't matter if you have been sliced by a chainsaw, shot by a shotgun or stabbed with a katana, you will still have full capacity like when completely healthy. Even if you have 1% of health, you will still be as good as new. But of course if your health meter drops to zero, you just suddenly die.
Corollary: Unfortunately your enemies possess this exact same property.
Corollay: There is no such thing as an "injury", either death, or perfect health.
Law of vertical stability
No matter how far you are thrown by an explosion or how high you fall from or how hard you are hit by enemy fire, you will always be able to stand perfectly vertical, without ever falling to the ground or even having to regain your balance.
Corollary: You will never drop your weapon either.
Law of infinite enemy ammunition
Even though you can run out of ammunition, your enemies can't. They have a magical infinite ammunition supply.
Corollary: Sometimes one of your own weapons has infinite ammo. Usually this weapon is the least powerful and least useful, though.
Corollary 2: If a weapon is fixed to the ground and cannot be taken (but can be used), it has an infinite source of ammo. This is because it's an enemy weapon and thus subject to the above law.
Law of reloading
Reloading half-full magazines is very easy and fast. This is so even if the magazines contain something more intangible than physical bullets (such as plasma charges).
If bullets are stored in magazines (instead of individually), filling a half-full magazine in the weapon with the ammunition from another half-full magazine (in hammerspace) is equally non-problematic. The on-screen animation will, however, always show you changing the entire magazine.
Law of crates and barrels
There are always crates and barrels everywhere. Always.
Law of exploding barrels
At least some of the barrels laying around will explode if you shoot them enough times. No logical explanation exists why there are so many exploding barrels laying around in city streets, hi-tec building complexes, etc.
Law of indestructible scenery
Most of the scenery will be completely indestructible. No matter how powerful weapons you have, even if these weapons can be used to destroy armored vehicles and enormously oversized alien monsters, trying to destroy a wall, or even a window or a wooden door is usually impossible.
Corollary: Law of indestructible obstacles
Even a simple locked wooden door is enough to completely stop you from getting to the other side without a key. It doesn't matter if you try to destroy the door with a bazooka or a plasma cannon, it won't budge. Never mind that this exact same weapon will be used to destroy armored vehicles and megamonsters.
Corollary: Trying to bypass the door by going through a window besides it will also by futile. The window is also protected by this indestructibility.
Law of useless obstacles
No matter how fortified a place is or how much security there is to stop invaders from passing through, there will always be a way. Indestructible doors will always have a key which can be collected from the side where you are in (such keys will never be on the other side which is completely inaccessible without it). Also, no matter how secure an installation is, there will always be an easy way of opening obstables by pressing a button or touching a computer screen. If nothing else, there will at least be a helpful NPC which will open the door for you.
Corollary: Law of obstacle visual clues
Obstacles (such as doors) which can be bypassed will usually have visual clues which makes them obvious and clearly distinguishes them from similar obstacles which are just part of the scenery and play no useful role.
Law of weapon perfection
Weapons never jam nor malfunction in any way no matter how much they are used. Rifles using telescopic sights will always be perfectly aligned.
Law of infinite stamina
No matter how many hours you run, jump, swim and perform other physical activities without rest, you will never get tired, you will never have to eat nor drink nor go to the bathroom and you will never have to sleep.
Law of anti-newtonian motion
Bullets always travel straight, without being affected by gravity. They also usually travel infinitely fast, without any delay between the shot and the hit, yet this doesn't cause any recoil whatsoever.
Corollary: The only possible explanation for this is that bullets have no mass and are completely impervious to air resistance. On the other hand, how massless bullets cause damage is unexplained.
Law of time dilation
The surrounding universe outside of the playing area is located at a different time level than the area itself. This means that no matter how long you play in that area, if the sky is visible, time of day will be static. Especially if the Sun is visible, it will not move no matter how many hours you play.
In a few cases the phenomenon is the opposite: Time outside the area will travel must faster than inside. If there is day and night, sunrises and sunsets, a whole day will usually take something like 30 minutes.
Law of enemy patience
Your enemies will usually be strategically located in the map, and will patiently wait there for your arrival, no matter how long it takes.
"My hands are full" law
Any simple tasks requiring the use of hands will usually be impossible. These include things like climbing chest-high walls or catching the edge of a pit to avoid a fall.
Corollary: Climbing ladders will usually be done without hands, while still holding your weapon (even if holding the weapon requires both hands).
