Concealment Equals Cover

""Thank God for these bulletproof tables they've got everywhere now.""

- Jigen, Lupin III (Geneon dub)

Concealment and cover are two totally different things. Yet Hollywood seems to get the two mixed up.


 * Concealment: You can't see through it. Walls, garbage cans, car doors, Bulletproof Human Shield, etc.
 * Cover: Stops bullets (and other projectile objects). Some concealment objects may stop bullets, depending on the object and the bullet. Others will not.

Hollywood seems to apply this trope most egregiously to car doors. Car doors are mostly plastic with a thin metal plate on the outside, designed to maintain its structure against broad and wide pressure of another car impacting it, but most certainly not designed to withstand bullets. Other than police cars which have been specially designed to withstand the impact, there isn't a car on the market whose doors could stop even fairly low-caliber bullets.

The trope also applies to buildings, however. A bullet will generally be expected to manage 12 inches of penetration in ballistic gel to be considered a useful defence load, and this will generally allow it to penetrate any interior walls of an average home; even special frangible rounds are only designed to be stopped by the heavier brick exterior walls so they don't exit the building and hit random passers by.

This trope is powered by the Rule of Perception; if you can't see it, you can't hit it. Of course, it's true that it's harder to hit something you can't see, simply because you can't be sure where it is; this trope is about anything opaque being effectively bulletproof. Related to Bulletproof Human Shield, with the eponymous Human Shield serving as the Concealment. If the bullet is stopped by some small object on the hero's person, that's Pocket Protector.

In Video Games, this can be considered an Acceptable Break From Reality in games with cover systems, since it would be frustrating to get into what appeared to be cover only to find the enemy could still hit you just fine; players tend to only object when things no reasonable person would try to hide behind like ordinary glass or picket fences are still totally bulletproof. It tends to be more of a problem when enemies can take cover in places that blatantly aren't cover, such as being protected from a hand grenade by hiding behind a rack of magazines or handrail.

This is common enough that only aversions, subversions and justified cases should be listed. Contrast with The All-Seeing AI, where concealment most definitely does not equal cover or concealment.

Also see Bulletproof Human Shield, when bodies are used for cover, and Bombproof Appliance or Improbable Cover, for when tissue-paper stops explosion.

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 * Played with in a recent ad that has the police take cover behind their squad doors (as noted above, those are designed to stop bullets), only for them to run forward to take cover behind a CARDBOARD BOX. Of course, the stupidness of that action was the point of the ad.

Anime/Manga

 * Justified in Black Lagoon -- the team's favorite drinking spot attracts dangerous weirdos from the whole neighbourhood, so the owner had his bar reinforced for use as cover.
 * Also averted during the "Baile de la Muerte" arc, when the US Army unit "Grey Fox" slaughters the mercenaries hired to kill them by shooting through the walls and doors.
 * Subverted in one One Piece movie, where new hero Shuraiya takes cover behind a table during a bar fight, and the bullets punch right through the table beside his head. He then uses the table more as concealment and keeps moving it so they can't tell where he is behind it. Interestingly, since they were firing flintlocks, the heavy oak table probably would have stopped the bullet in real life.
 * One issue of City Hunter, with a criminal in a cafe who tells Ryo he can't shoot him - because Ryo's gun is so powerful, the bullet will go through him and the window behind him, and risk hitting an innocent bystander outside. Ryo shoots through his own hand to slow down the bullet enough to avoid this.
 * Lampshaded in Hidan no Aria, where Aria and Kinji take shelter from a storm of bullets inside a wooden vaulting box... which Aria quickly reveals to be bulletproof.

Comics

 * Averted in issue #53 of Garth Ennis's run on The Punisher. The Punisher and Barracuda take cover behind their respective cars, but the artwork clearly shows the bullets easily punching through.
 * Hitman. Diving behind the bar in a dive would usually help as your opponent wouldn't quite know where to blast. However if he has X-Ray vision...

Film

 * Averted in Real Genius. The finished prototype laser goes through the blast shield, three walls, a statue, a billboard, a tree, and continues all the way to town.
 * Averted in The Terminator. When the Terminator attacks the police station, he shoots a cop right through the wall, as a cop realizes standing in the doorway is not a good idea and ducks behind the wall.
 * Averted in the shootout from The International. One of the guys gets shot through a dresser he was using for cover.
 * Averted hard in Live Free or Die Hard, in which the two main characters are shot at not only through the window, but through the building's exterior walls.
 * Harder when McClane shoots the Big Bad through himself.
 * The aversions have existed since the first film, including one scene where McClane shoots a mook through a table.
 * Also averted in Book of Eli, in pretty much exactly the same way as the Die Hard example.
 * Averted in Snatch, Tony shouts through the wall for his boss to duck, then empties the magazine at body height through the wall. He successfully hits two of the four guys in the hallway besides his boss, and the other two decide to scram.
 * Averted in an almost identical way in The Matrix, where Agent Smith fires through a wall to hit the leg of an escaping Morpheus.
 * Averted in The Professional. Matilda's little brother runs from the corrupt DEA agents, one of them starts spraying through the wall with a kimmel ap-9 and manages to hit him. Later, when the police try to storm Leon's and Matilda's hideout, the bullets go through the wall, which makes the situation rather sticky for those inside.
 * In Mr. and Mrs. Smith, Brad Pitt takes shelter from Angelina Jolie's UMP 45 by hiding behind a fridge door.
 * Averted somewhat in Lethal Weapon 4. Riggs kills a man who was hiding behind some pipes, by using another pipe to deflect the bullet so the hiding guy stands up from the pain of getting shot.
 * Averted in Miller's Crossing, when The Dane shoots a thug through the wall.
 * Averted in Death Wish 3: when a mook hides behind a garbage can, Paul Kersey (Charles Bronson) shoots at him with his .475 Wildey Magnum (which is the most powerful semi-automatic pistol in the world, even more powerful than the Desert Eagle). The bullet goes right through the garbage can and hits the mook (Kersey puts another round into him anyway just for good measure).
 * Averted earlier in Death Wish II when Paul shoots Cutter as he tries to retreat while holding his boombox in front of his face. Kersey's bullet goes right through it and catches him between the eyes.
 * Alien Nation had bullets piercing all the way through a car (and the guy hiding behind it), but the bullets were revealed to be special, industrial-strength Dakka.
 * Averted in Saving Private Ryan, when a German soldier is killed through the interior wall of a building.
 * Subtly averted in Lord of War. The mobster who hides behind a restaurant table only has his luck to thank for escaping the assassination attempt. When we're shown the scene from behind him, it's clear the table has been shot clearly through - he's only alive because the gunmen are woefully incompetent and have sprayed and prayed instead of shooting the table in the centre.
 * Tremors 2. More Dakka kills the monster of the moment...and the escape vehicle that was behind several walls. Oops.
 * Parodied in I'm Gonna Git You Sucka: at one point, the hero takes cover behind a ckicken wire fence.
 * Averted in Bullshot (1983). The hero blasts away at a huge tarantula crawling across the floor, nearly killing several people in the dining room below. He then spends several minutes running about searching for the 'mad gunman' who's just shot up the place.
 * In the climactic gunfight scene at the end of The Shootist, J.B. Books (John Wayne) kills one of the bad guys (Richard Boone) by shooting through the barroom table top which the bad guy is holding in front of himself.
 * Green Hornet. One of the reasons the heros even consider being vigilantes is because the genius sidekick is very efficent at bullet-proofing cars. Then they invent offensive weaponry that requires them to open the car doors.
 * Grosse Point Blank has John Cusack evading bullets by hiding behind a rack of potato chips.
 * Averted twice in Magnum Force when Harry shoots a hijacker who is hiding behind a thin partition in a airliner; and again when a cop is shot through a door.
 * Subverted in Sahara

Literature

 * In Red Square, a novel by Martin Cruz Smith (one of the sequels to Gorky Park), a German police officer opens fire on a group of suspected assassins (working for The Mafiya) without ever seeing them. He simply unloads a submachine gun through the wall. And then proceeds to do so again, aiming lower in case any of them decided to go prone. He doesn't report this, as his superiors might object to him just gunning down someone without warning or even seeing them.
 * Averted in the Discworld novel Men At Arms, when Vimes is attacked: The Gonne clearly shoots through walls, and Vimes has to outwit its wielder.
 * It's explicitly noted that it is only a "lath and plaster" wall, and he knows this thing shoots heavy, lead projectiles with enough force to go inches into oak flooring...
 * What's really great is that he has to outwit his assassin twice - the assassin knows the old "use an arrow to hold your helmet up" trick. Vimes uses a pole used for opening windows.
 * Justified at least once in the Star Wars Expanded Universe - Genre Savvy cantina owners are known for using reinforced chairs, tables, and such so that they won't have to replace it all after the Inevitable Bar Fight.
 * Averted in the Spy Fiction novel "Running Blind" by Desmond Bagley, where the protagonist gets his hands on a high-powered sniper rifle and uses it to shoot through the walls of the house his KGB opponents are in, killing or wounding everyone inside.
 * Justified in many of David Drake's novels. Plasma weapons lose containment if they hit anything but air, so even a twig will stop a plasma cannon shot. Once.
 * This only works if you're way behind concealment. Hitting light cover doesn't "stop" the shot, it detonates it at that spot.
 * Subverted in Retribution Falls by Chris Wooding. An enemy mook hides behind a large but empty wooden crate and is promptly shot dead.

Live Action TV

 * Justified in The Sarah Connor Chronicles. The first episode features a Terminator discovering the Connors' new apartment, and a shootout ensues, during which Sarah uses a recliner as cover, successfully. A couple scenes later, the police are examining the apartment and discover the chair had been lined with kevlar.
 * Averted in one episode of CSI; a little girl is killed by a stray bullet from a drive-by, despite being inside her house ducking sensibly under the bed.
 * In an episode of Bones, a Genre Savvy bad guy is taking cover behind a heavy steel door, only to learn that the Hand Cannon that he had mocked Agent Booth for carrying was sufficiently powerful to penetrate through the door and hit him anyways.
 * One episode of 24 involves Jack and a hostile both taking cover behind various interior structures. Jack pops up from behind his railing, and shoots through the pillar his opponent is hiding behind, killing her.
 * Averted in Stargate SG-1. The heroes use C-4 to open a blast door (two blocks, because it's a blast door). The people trapped inside overturn a table to hide behind, but a massive spike of door is embedded in it anyway, nearly skewering someone on the other side.
 * Averted in this scene of Breaking Bad.
 * The pilot episode of Burn Notice lampshades this with a drug dealer's apartment, who has a reinforced door. Michael explains that most people ignore the fact that most walls are just drywall and plaster, which he uses to shoot the dealer in the knee from outside. Michael and Sam later deliberately armor a car with phone books and bulletproof glass, expecting to be hit by a gang. The outside of the car is still riddled with holes but none penetrate inside.
 * Myth Busters demonstrated that a car door stuffed with phone books will stop bullets fired from handguns.
 * The Buffy the Vampire Slayer episode Homecoming has Buffy trick the pair of assassins hunting her into shooting each other through a wall.
 * In the 2010 Top Gear Christmas special, the boys were instructed to drive through the worn-torn Middle East to Bethlehem. Security was high on their mind, and they drove around in Kevlar vests and helmets. At one point, Jeremy has an idea to stuff his doors with sandbags for additional protection. However, a 9mm handgun (albeit fired at close range) went through the reinforced door and out the other.
 * Taken to extremes in the Top Gear Range Rover vs. Challenger 2 main battle tank. The rules of the game: Jeremy has to escape and evade a single Challenger 2, traversing the Challenger's own training grounds of the Salisbury plain. The tank's job is to score a simulated kill on Jeremy using the tank's 120mm main gun. (allowing the crew to remember that they also had two 7.62mm machine guns and personal sidearms, although both are shown in the opening briefing, would have made it far too easy). Jeremy then proceeds to hide behind a bush before recalling the difference.
 * Parodied further in this machinima of the show, wherein the bush he hides behind provides neither cover nor concealment.
 * An episode of a TBS show called Worst Case Scenarios (based on the Worst Case Scenario Survival Guide and starring a guy named Mike Rowe) featured a scene with a man taking cover behind a concrete pillar during a parking garage gunfight. We see a bullet hole burst through the pillar at head level, a few inches to one side of him.

Oral Tradition

 * Averted with a legend from the Wild West. While staying at an inn, a gunfighter in Texas, kept awake by loud snoring in the room next door, fired his gun through the wall and killed the culprit in his sleep.

Tabletop Games

 * Warhammer 40000 has a variation - while fortifications made to absorb attacks provide an excellent 'cover save' protection from ranged attacks, things like really high grass can still provide a lesser one. The rules explicitly say the reason for that is how it would make the victim of a ranged attack harder to target. It gets stranger with other units - units in front of other units provide a small 'cover save' for the units behind them, since they are in the way which makes it harder to hit the ones behind, even if the ranged weapons in question should be capable of annihilating the units in the way and then strike the ones behind them (there are no other rules for it, so a successful cover save in this manner would have no chance of harming the units in front of the others. An unsuccessful one would just have the units behind be hit.)
 * This (4+) cover save isn't small; it's as good as the save granted for holing up inside a building or hiding inside a treeline. Human Shield indeed! It's Handwaved with a "fouled aim" justification, and rarely justified why the enemy simply didn't shoot anyway.
 * And due to the fact that the narrative tabletop game Inquisitor might have only a handful of models in a given game, it can go into minute details. A character can take cover behind a wall, crate, fortified bunker or whatever they're near - it simply absorbs part of the damage from the shot like an additional layer of armour, so a person hiding behind a wooden crate and being shot at will almost certainly still be hit, but the crate will absorb some of the power and do marginally less damage (or, if they're really lucky, deplete enough of the energy and cause the shot to then deflect off their personal armour)
 * Warhammer Fantasy makes cover more difficult to hit a given unit with missiles (in the case of solid walls because they can duck, and in the case of "soft" cover such as fences or bushes because it's harder to hit something you can't see clearly), not to damage, and sometimes is ignored totally in some cases. So a unit behind a wall might be hit less often by the average guy with a handgun, but a superbly trained assassin will most likely not be bothered that much, and a gout of flaming chemicals will just roil over the cover. Units interposed between the shooter and victim unit have the same penalty as a brick wall because the firing unit either is put off by the nearer enemy, or has to stop themselves from accidentally firing into their own soldiers wandering into their sights.
 * Averted for unintentional hilarity in D&D's 3rd edition (and its many spinoffs): Cover and Concealment are entirely separate systems, with Cover giving a bonus to your Armour Class (with the logic that cover blocks some attacks completely), while Concealment gives a random, percentage-based chance that the attack missed (since it just makes aiming at your real location harder). The humour here is that, against a sufficiently skilled enemy, the bonus to armour class can be made irrelevant by a good enough attack, while the miss chance is virtually always relevant, so under some circumstances, having half of your body obscured by mist or swaying tree branches is better protection than having half of your body behind a stone wall.
 * The exception to this is 'total cover', which is when you are, well, totally covered by something that blocks line of sight (like standing behind a stone wall that completely obscures you from your foe). Characters behind total cover cannot be directly targeted or attacked.
 * GURPS specifically notes that penalties from the target's cover are dependent on your weapon: A small pistol can only hit a driver's upper body (-4 to hit), but a machine gun or rifle can hit normally (at most a -1 to guess where the victim's vitals are)

Video Games

 * In a particularly ridiculous example, in Metal Gear Solid: The Twin Snakes, you are attacked by a boss piloting an M1 Abrams tank firing high explosive rounds. You can avoid damage by hiding behind a snowbank.
 * Avoided in John Woo Presents Stranglehold, powerful weapons can - with repeat fire - tear through many walls and columns, including reinforced concrete in some cases. Means you can't hide behind that flimsy pillar forever...
 * Call of Duty: World at War and the Modern Warfare series allows you to shoot through certain objects (such as wood) with some reduced damage from the bullets; there's no system for actually destroying anything, though, and any form of divide between the player and the explosion will stop grenade shrapnel dead. In the singleplayer, this only benefits you however. The enemy NPCs simply can't damage you with cover in between you and them.
 * What is and is not bulletproof however seems to be completely random at best. In some places, thick, metal and concrete walls can be shot through for massive damage, but nowhere is there a melon leaf that can be penetrated by an anti-tank rifle in the first two thirds of the Modern Warfare trilogy.
 * Battlefield: Bad Company included a environment destruction system for breaking down things to hit the enemies behind them; though mostly just wood was easily destroyed from bullets, and explosives were generally needed to damage most things.
 * The sequel is even better about this, with almost no cover being permanent. An easy way to destroy an enemy objective guarded by hostiles in the same room is to destroy the entire building.
 * Battlefield Heroes, on the other hand, makes all the scenery indestructible. Might be considered a Justified Trope since the game is made for casual players who might not have the hardware for such a thing.
 * Averted in Counter-Strike, where guns of sufficient power will penetrate some materials.
 * Dawn of War 2 has pretty much everything short of the ground providing cover bonuses - some stuff could justifiably be so, like plants that may be really tough due to being fictional. On the other hand, the barrels seem to be rather unlikely. Presumably, it uses the same justification as the original tabletop mentioned above.
 * It should also be mentioned that the ground can indeed provide cover bonuses provided you shell the area with high explosives prior to moving in. The troops will hunker down in the resulting craters.
 * Company of Heroes has the same cover system as Dawn of War 2, but letting wooden things provide cover bonuses is probably less justifiable to most people. Try to by assume the same potential explanation from Dawn of War 2.
 * Averted in the sense that ordering your men into flimsy cover is generally a very bad idea; it's relatively poor protection and will fall apart pretty damn fast under heavy fire. Applies to everything once the enemy starts getting tanks.
 * Units in the game have different levels of cover. Red being exposed, yellow being partially covered (reduced damage from small arms), green means fully covered (small arms can't do a damn thing, but explosions will hurt)
 * Somewhat averted in TimeShift of all things. Some cover will disintegrate under heavy fire, other times enemies will simply lob grenades or run to a better spot to shoot you. Boxes can also be knocked over, collapsing your cover.
 * In the X-COM series, most objects or buildings on the battlefield will stop at least one bullet, usually getting blown to bits in the process. Shame the aliens tend to fire on full auto. Cover will not make you immune from explosives so a standard tactic is to just blast any building with high explosive rounds, rockets and grenades.
 * Annoyingly Averted in STALKER, most noticeable in the second level of the second game, where you have to run from a mounted machinegun capable of killing you in less than a second. Annoyingly because even through an entire tree, while the bullet trajectory and speed are reduced by a great deal, so much so that you can see them dropping to the ground, the bullets still do the same damage as when they were full speed. Made the area into That One Level.
 * Super Mario Bros. 3 has those white blocks. If you duck on them for a few seconds, you can go behind bushes and the like and enemies won't be able to hurt you as long as you're totally concealed. Yet if part of Mario is poking out, he can get hurt.
 * Averted to the benefit of the player in Left 4 Dead. You can damage zombies through walls, furniture, and even other zombies.
 * Gears of War has destructible cover (like wood) and completely indestructible cover (pretty much everything else). Even a wardrobe will stop bullets until it's destroyed though.
 * Taken to an extreme in the Jet Li game Rise to Honor. During the gunplay segments you can hide behind anything (even garbage cans) while mooks shoot at you with their infinite ammo guns. You could literally hide behind a garbage can forever without ever taking damage.
 * In the very first level of Psychonauts, you come up against a machine-gun bunker that can shred you to bits in seconds. Although you can activate a series of walls to serve as cover, nearly all of them save one are made of wood, which is destructible, and lasts only a second or two under the intense gunfire. However, this level is in one of the characters' dreams, where concealment = cover makes much more sense.
 * In World of Warcraft, you can't even attempt to shoot or cast spells at anything that's out of your line of sight, which includes walls and such. What's odd about this is that some terrain features that you'd ordinarily expect to block line of sight, like trees and hills, don't, so you can shoot through them as easily as through air. Similarly, if a unit moves behind an obstacle after a projectile is launched, said projectile will happily curve to follow them even if it means passing through solid obstacles.
 * Half Life 2 mostly plays this straight, but thanks to the Havok physics engine, allows objects being used for cover to themselves be used as weapons. Hide behind a stack of barrels, for example, and a charging Antlion Guardian will bash right through them to get at you. Hide behind a car, and it'll throw the car at you.
 * Also, the patches of aluminum siding used as cover during the Strider fight at the end of Episode One do protect you from the minigun used by the Strider, but the siding can and will fall off after taking so many shots, exposing you to the Strider (which you were exposed to by climbing the ladder to the platform with the siding). At one point during the chase building up to the fight you can hide behind a shipping container. Sadly you cannot hide behind it for long as once you get behind it the Strider will try to kill you by shoving the shipping container into the wall behind it with its beam attack. The only part of the platform during the actual fight that you can reliably use as cover is the stone support beam just prior to the siding panels, from which you can reload the rocket launcher by grabbing stray rockets on the ground with the Gravity Gun (as the siding panels come off you will be exposed if you go for the ammo crate and if you're a good enough shot with the rocket launcher you should only need at most six rockets; possibly less if you scored successful hits on the Strider on the way to the platform with rockets or thrown Hopper mines (the Strider performs its hit animation when hit prior to reaching the main arena of the fight but it's not clear if the Strider's health is actually reduced).
 * Army Of Two would have you believe a car door will protect you from rifle fire.
 * Averted to the ridiculous extent in games using the Silent Storm engine, developed by Nival Interactive, such as Silent Storm, Silent Storm Sentinels, Hammer And Sickle, Night Watch, and Day Watch. Any object is destructible with sufficient firepower. While a wall may stop a bullet, it will be destroyed with several more, making cover irrelevant against heavy-cal guns. In fact, continuous fire from such a weapon can easily collapse an entire building, especially when wearing a Panzerklein.
 * Never mind the explosives, which will also level buildings when used.
 * Averted in Crysis, in the same manner as the Silent Storm examples above.
 * Averted in Killer 7, when  hides in a dresser to escape  . It does her no good.
 * Averted in Black. Anything that can be hidden behind can be destroyed by gunfire. The game's main marketing point (apart from Gun Porn).
 * Scarface the World Is Yours. Shooting out the window of a well-armored car is a great tactic...oddly, your lackey in the passenger seat will (quite possibly) get ventilated and die while Tony remains untouched.
 * At one point in Resident Evil 4, you can hide in a TENT to block bullets from a GATLING GUN.
 * In Rainbow Six 3: Raven Shield your bullets will pass through glass and chain-link fences, unless you load them with hollow point ammunition, in which case a chain-link fence is effectively bulletproof, but only to your weapons and not those of any terrorists. Glass will similarly block a hollow point round, although it will break and allow subsequent shots to pass through.
 * In Time Crisis, being behind cover protects against grenades and rockets. The enemy Mooks fire/throw them directly at your face, not at the crate you are hiding behind.
 * Averted in World of Tanks - if an enemy tank spots you behind a bush or fallen tree they can fire straight through at the thoughtfully provided outline the game shows them of your tank.
 * Played completely straight in Mass Effect 2. Archangel's recruitment mission features indestructible sofas that a gunship cannot penetrate with missiles, let alone normal guns.
 * Mass Effect 3 averts this with Armor-Piercing Attack that can penetrate some cover. In fact, with enough penetration enhancements it is possible to shoot clean through the floor or walls (though only the geth multiplayer characters really benefit from this: in Hunter Mode they can see enemies through solid objects).
 * Straight in Team Fortress 2 as well. A source of much hilarity on newcomers is that chicken wire counts as "cover", and so you are unable to shoot through it.
 * In Indiana Jones Greatest Adventures, the Club Obi-Wan stage has a Crosshair Aware Indy taking cover behind tables and grand pianos.
 * In Fallout 3, it is prefectly permissable to take cover behind lamp posts or thin trees in order to block gunfire as long as you're standing directly opposite the opponent, even though you should be broader than the cover. Many enemies may even lose track of you if they can't make direct eye contact. It's far from uncommon for a supermutant with a minigun to run up and look for you behind a lamp post. (Although supermutants aren't known to be very bright, so it fits.) Also, due to the general lack of destroyable landscape objects, everything is bulletproof and only takes a few cosmetic bullet holes.

Web Comics

 * In A Miracle of Science, Agent Prester gets in a gunfight with a mafioso in a cheap diner, and dives behind a turned-over table for cover. The wiseguy then proceeds to simply shoot through the table while making snide comments about how stupid it is to hide behind 'a flimsy fiberboard table'. Prester gets a bullet through the shoulder, but fortunately, he's Made of Iron...
 * About to be averted in this comic on badspot.us in 3, 2, 1....
 * Played entirely straight in all Might and Magic games. Might And Magic 8 has the possibility of an explosive fireball being stopped by a tent. That's right, a (theoretically) flammable material stopping a ball of explosive flame. With no damage to anything inside.

Real Life

 * Justified in places where houses have interior walls as strong as the exterior ones, like large swaths of Europe.
 * While light concealment may not stop bullets, it increases your chances of surviving since the person shooting can only fire where they think you are behind the cover. Also, lower caliber bullets can be blocked by less than what a larger caliber can go through. However, one should try to get behind the thickest piece of cover one can.
 * It is also sometimes true with hollow point bullets that are designed to fragment upon hitting solid objects to avoid overpenetration. It is even more true with frangible bullets that are used by anyone who wants to avoid putting holes in things they otherwise shouldn't, most notably by air marshals.
 * Bullets will, of course, lose velocity traveling through concealment, possibly reducing the impact velocity enough to make a difference. Unfortunately, this difference is more likely to be that the bullet will get lodged in the victims body rather than pass clean through, adding the dangers of having a foreign object in their body to the regular problem of having holes torn into it. It's fairly unlikely for any kind of concealment to reduce bullet velocity enough to meaningfully reduce (or affect at all) the damage done. Hence, this trope.
 * It can make the difference when the target is wearing armor, with the concealment reducing the velocity of the bullet just enough to allow the armor to absorb the shot. Still unlikely for most forms of concealment, but unlike above the difference between 'penetration' and 'no penetration' is much bigger (and more positive) than 'pass through' or 'lodged in body'.