Cardboard Obstacle

""As you use your Fire Arrows to light the four braziers in this room, take a moment to reflect on how insulting it is that I keep pointing out that you need to "light all the braziers" when you're in a room that clearly contains nothing except unlit braziers. Anyway, um... Light all of the braziers (sorry, it's my job) and the chest containing the Mirror Shield will appear.""

- Casey Loe, Versus Books' The Legend of Zelda Majoras Mask Strategy Guide

Back in the good old days of video games with true nonlinearity, you wouldn't get far before finding many of your possible paths blocked with certain types of obstacles. Trees. Rocks. Ice cubes. You've seen them all, and you know exactly how they work. Somewhere along the line, you'll eventually acquire an item that will allow you to bypass these obstacles. A candle to burn down bushes. A hammer to smash rocks. A magic wand to melt the ice.

It was an ingenious concept. It regulated the game's pace wonderfully and also encouraged backtracking in search of those opportunities to open new paths. These are generally Insurmountable Waist High Fences, and the items needed to bypass them are usually available only when you are genuinely able to survive what lies behind the obstacles.

Between then and now, something went horribly wrong.

Those trees, rocks, and ice cubes are still around and probably won't be leaving for a long time. They still work exactly the same way. What's wrong, then? They have become frivolous Cardboard Obstacles; it's no longer a real challenge to get the item to get past them. And if there is no challenge to get the item, then you have to get the XP to get past the stronger monsters in other, more boring ways.

Cardboard Obstacles manifest themselves in three main ways:

Remember Your Inventory!
This is when an obstacle of this sort pops up and the game expects you to already have the item to remove it. The challenge is no longer to get the item, but to remember which item it is and hope you haven't thrown it away between acquiring it and reaching the obstacle. Thus, there is less challenge; you are not going to level up while hunting through your inventory.

For instance, say you're dungeon-crawling and you come across a cracked rock blocking a door. All you have to do is bomb it, and so you do. But this is the final dungeon, and (most critically) you had to get the bombs in your inventory before then. So, what's that rock doing there, besides forcing you to use up a perfectly good bomb?

It's only there to remind you that you have a bomb. And if you don't have the bomb, then it's too late to get it and the game becomes Unwinnable.

No puzzle. No thinking. No backtracking. Just open your inventory and blow up the rock. It's not like you have a choice.

On the bright side, reminding you that you have bombs may be a clue that there might be secret rocks or that the boss may be vulnerable to explosives.

Failure at Nonlinearity
This is when obstacles that can be removed block only the relevant path forward and effectively mark it. Perhaps the game designers aimed for Zelda formula, but missed.

For instance, you finally found the bombs that will get rid of the rock blocking a room exit. You step out of the room and find a small group of connected rooms (including a plot-critical item) and a rock blocking a path forward. Awesome, you can blow it up. It leads to a tunnel blocked midway with another rock, which would effectively be a dead end for you if you had no bombs. This tunnel ends in a room in an old section, but the rock had looked like a wall from the other side. If you look very carefully, you will see another rock, which leads to a shortcut to another old room; then there is another rock, behind which is the room with the pumpkin smasher to get rid of the pumpkins blocking the branch in the tunnel...

And that's it. No more rocks in this section or any other in the normal game. And no new caches of bombs at all.

If an item is this sort of thing, then it will prove useless after you leave the section where you found it. There may be an obstacle much later to punish you for getting rid of the thing once it appears evident that there are no more obstacles to destroy with it.

That's how many obstacles work in modern games. They're all placed directly in your path. You will see and destroy them all during a normal playthrough. And there will be no false leads—no paths with obstacles but without anything important behind them.

En Masse
There are entire rooms filled with cracked rocks blocking the main path. Or long hallways turned into dead ends every few feet by rocks. And you can only destroy one of them at a time.

The developers think it's funny, but you can only groan. The obstacles are a waste of your time and theirs when used that close together that linearly. Try not to imagine how much sooner you'd be in the next room if it weren't for them all, or you'll only make yourself cry.

Examples

 * Pick a Pokémon RPG. Any of them. The Cut HM, and several others - Rock Smash, Waterfall and Whirlpool spring immediately to mind.
 * What's especially annoying is that you can't delete HM moves until way late into the games. Now this might make sense if HMs were single use like TMs, thus capable of rendering the game Unwinnable, but they aren't -- thus making the whole damn thing an exercise in frustration. However, this did prevent players from making the game unwinnable via, say, flying to Cinnabar Island and releasing all Pokémon that knew Surf or Fly and losing all one's money and Poké Balls, thus making escape impossible unless one got lucky with trading. There is another restriction in place in more recent games for presumably the same reason: you can't delete an HM move if that's the only Pokémon you have that knows it, and you can't release or trade away such a Pokémon either.
 * The first game also had trees scattered throughout, far past the point that you would have acquired Cut. This gimped your Pokémons' fighting capabilities since Cut is a rather weak move.
 * Generation 5 stopped this from being a true Scrappy Mechanic because trees don't grow back for 24 hours and strength-moved rocks stay in one place if you push them in a hole. In fact, strength's point has switched to that. You aren't just moving rocks out of the way anymore, you're now pushing them into holes to function as makeshift bridges. The only other HMs that you'll need consistently are those that are at least somewhat useful in combat, like Surf and Fly.
 * At the very least, even in previous generations, Cut, Whirlpool, and Rock Smash were only required for getting to new areas fairly infrequently, but are still pretty frustrating for players who want to go after all the optional items, and Surf, Waterfall, Fly, and Strength were still decently-powered moves for battle. Flash, Dive, and Defog, on the other hand...
 * The Legend of Zelda Twilight Princess is full of these:
 * A while after receiving bombs, you encounter barriers they cannot destroy, so you get the Ball and Chain, which can break them, but also makes your bomb supply mostly pointless (they can still be used for arrows). And in the next dungeon, there are barriers the Ball and Chain can't destroy, so you need to get a Living Statue to smash it with a hammer.
 * Pretty much all bombable walls are like this, since there's usually a crack in the wall that signals that the wall is bombable. On the other hand, exceptions to this can be very frustrating. The room with the wall is about four minutes in.
 * While the Dominion Rod was put to ingenious use in the level it appeared in, it had no function outside that level except for 5 statues scattered across the land, as well as a token usage in the penultimate dungeon. Once all the statues have been animated and their items taken, the rod serves no purpose at all, laking even the token offensive capability of most Zelda tools.
 * The slingshot is rather useless, and mostly present as a reference to The Legend of Zelda Ocarina of Time, since you acquire the bow soon after, which has all the capabilities of the slingshot as well as being a much better weapon.
 * While the dungeon you get the spinner in makes very liberal use of it, tracks for it only appear here and there in the dungeon, and since you need the tracks for any serious use, it's "remember your inventory" from the moment you pick it up. The only minor thinking part comes when you encounter spinner-shaped holes in a later dungeon instead of tracks. Oh, and some tracks on a cliff make it helpful for quick transport.
 * In the eighth dungeon of Oracle of Ages, the boss's door is blocked by four obstacles, each of which requires a specific inventory item you already have. However, the obstacles do serve another purpose, in that the order of the inventory items needed to remove them is the order of the inventory items needed to defeat each form of the boss.
 * The NES game Battle of Olympus had a handful of these, in a very Zelda fashion. One item slightly subverts this: the staff of fennel after receiving Prometheus' ability to shoot fire. Not only could it clear away dry shrubbery, the fire it shot could also do damage to many enemies.
 * Most Metroid games avert this. They usually do so by making items that allow you to pass certain obstacles inherently useful in and of themselves. Missiles that open doors also kill things faster. The Screw Attack that allows you to pass certain kinds of blocks also kills any non-boss enemy in one hit. The Space Jump is used constantly for basic movement. And so on.
 * Most of the times when Metroid games use this trope is when one item trumps the use of another. For example, in Super Metroid, once you have the Space Jump, the Grapple Beam is utterly useless. Through skilled use of various abilities, one can even avoid seemingly required items. The other times when the games invoke this trope are when a powerup is only useful in conjunction with an external object. For example, the Grapple Beam is nothing without grapple-points/grapple blocks.
 * Nothing apart from its infamous use to fry one of the 4 big bosses.
 * The Metroid Prime series had some problems with this when it came to translating the powerups to a 3D games. The spider ball in Metroid II, could be used to climb any wall, but the prime games, you can only use it on a few special tracks. Instead of being one of the most useful items like in the 2D games, the screw attack is just the way to get by a couple obstacles. Prime 3 is better about avoiding it, in that the grapple-based powers can be used for combat.
 * Used without becoming a pain in the ass in Half-Life 2: Episode 2 and Portal, to keep the player from charging forward and missing important dialogue or cool scenery, and mentioned as such in the commentary.
 * Final Fantasy Mystic Quest occasionally got a little too enthusiastic about blocking your path with mushrooms or trees (that must be cut down); adding to the "fun", they respawn. On the other hand, your tools for clearing obstacles are also your weapons.
 * Mario and Luigi: Superstar Saga is good about preventing this, but still has one instance of it. Right after you get your hammers, you can break the rock that Fawful places in your path. 2 screens later, you're in an area full of rocks, one of which is on fire. After that area, you find rocks blocking a cave entrance. After that, you play the mine cart minigame. After that, even more rocks.
 * One of the Ratchet and Clank games had a teleporter that only had two places it would be used. Worse, the second place was actually harder to get past by using it.
 * Just about any of the equippable "gadget" items are useless outside of the puzzles they solve. Insomniac finally relented around the third game, by making far less gadgets, combining the functionality of a few fan favorites, and letting Ratchet use the Refractor to fry gunships with their own beam weapons.
 * Hype The Time Quest and it's annoying fires. About a quarter through the game, you have to get ice magic in order to pass by flames to rescue your sidekick, Gogoud. You use it twice in the first fifty game-years.
 * And for the next fifty years, you don't use it until you are invited to the champion's secret room which happens to be behind a fire. Once again, two fires in fifty years. The second is in your sidekick's secret room where a flame magically pops up in your path. Fifty years later, you need it to get out of your own bedroom!
 * These show up in several different forms in Theresia. For instance, one hallway has five rocks that need to be destroyed with grenades or a hammer. You don't get the hammer until much later than when you can first reach the rocks, and you can only carry two grenades at a time, so you'll need to backtrack to the grenade stockpile at least twice.
 * Final Fantasy Adventure for the Gameboy loved this. Plants blocking one of your possible paths? Guess who's getting a new sickle weapon in the next dungeon? A chasm with a pole on the other side? Good thing the next evil castle has a flail you can use to grapple across such things. One notable case is with the cracked wall hidden passages. Earlier in the game, you break them with one-use Mattocks, purchasable at an item store. Later on, there's a cardboard obstacle in the form of a whole bunch of cracked walls. Woe be to the adventurer that, rather than searching and finding the reusable Mattock-like Morning Star, instead simply buys stacks upon stacks of Mattocks...