Already Done for You

A Plot Twist where another character in the story has accomplished one of your mission objectives for you. Unfortunately for you (or fortunately, depending on how you look at it), getting to the point to receive the MacGuffin or benefit is just as hard as accomplishing the mission yourself.

Not to be confused with Bait and Switch Boss, which is slightly similar and explicitly involves fighting a replacement boss.

You may have to do an entire dungeon to get to one of your objectives, only to find out that someone else's done it.

Contrast with Already Undone for You.

Film

 * In Indiana Jones and the Last Crusade (which also contains examples of Already Undone for You), Indy passes all the challenges set before him to reach the Holy Grail. A few seconds later, Elsa and Donovan enter the Grail chamber, Indy having been forced to show them the way. For the sawblades, Indy had thrown a convenient rope over the gears, causing them to freeze. They watched him as he walked over the name puzzle, so they just followed his steps, and Indy tossed gravel on the "invisible" bridge, showing them where it was.
 * In Jarhead, the protagonist gets the order to snipe one of the enemy officers when he arrives in a control tower. Said sniper's spotter is quite excited, since they'll finally get their first kill (they hadn't fired a shot in anger for the whole movie). The set up a perch in a nearby tower, and wait for hours. Finally, the target appears. The sniper consults his partner who confirms the distance, adjusts his scope, gets the green light...then a Major pops in and calls off the shot - saying that they're just going to airstrike the tower. This cues the spotter to beg for the chance to shoot, saying it won't make a difference either way, but no dice.

Literature

 * The end of Harry Potter and the Half-Blood Prince. ? Didn't see that coming... Of course, they still had to go through hoops to in the seventh book.
 * In the first book, the only Stone guardian that doesn't play to one of the protagonists' strengths, a big troll, was knocked unconscious by the villain they're chasing, so that all they have to do is run past it. This and the potion puzzle (which resets itself) were removed from the film, as they cut the tension. The first guard was also taken care of, but it didn't stick. The task of picking out the real key from the fake ones is also made easier since the villain somehow got it on the first try, marking it in the process.
 * Memory, Sorrow, and Thorn series:
 * In Andy McDermott's The Tomb of Hercules, the tomb has a series of traps based on the Labors of Hercules. About half of them have already been set off by earlier adventurers, allowing the heroes to waltz on through until they reach a point that no previous explorer has survived to see.

Video Games

 * A suspicious number of characters in the first two Banjo-Kazooie games offer you "this shiny thing I found earlier" (or some variation thereof), and that "shiny thing" always happens to be one of the jigsaw pieces you are after. They will sometimes specify where they found it, and in these cases it will always be somewhere the player can very easily reach, meaning had the heroes arrived a little earlier, there would have been an easy jigsaw to grab. Even some of the good guys who want Banjo and Kazooie to succeed in killing the witch will have these Jiggies, and will extort the player for them by forcing them to perform some mundane challenge, most often collecting [number] [object], before they will cough up the puzzle piece, even though according to their positions in the story they want you to get as many Jiggies as possible. (These challenges are sometimes fun, however.) Essentially, they've done the job of finding the jigsaws for you, but want you to do even more than they had to in order to get it from them.
 * Early in Chrono Trigger, Crono gets arrested, and since he's scheduled for execution in three days even if you were found not guilty, most players have him escape from prison, causing the trope to be inverted when Lucca shows up to rescue him. No need, Lucca, it's Already Done for You. On the other hand, if you don't escape in the (relatively short) three days, she does rescue you, and the guards you have to fight on the way out are Already Beaten For You.
 * Crysis takes obvious measure to avoid Escort Missions as you will either have allies rescue them after you get to them or the hostage will die anyway in such a way that it is not your fault.
 * In the Saturn Action RPG Dark Savior, depending on how you play the intro chapter, the rest of the game plays out in one of three different ways. In the first one, you go through a set of ancient ruins, solving puzzles to go through each room. However, in the second one, two other characters have passed through right before you, thus all the puzzles are already solved and you can just waltz through. However, this means you don't get to learn the history from the murals, as those are the barriers that move out of the way when you finish the puzzles.
 * Disgaea 2: Cursed Memories takes this to ridiculous extremes by having Etna casually swing by to let you know she's already killed the final boss..
 * In Double Dragon 3 on the NES, Hiruko informs you, after you obtain the second Sacred Stone, that she has the third one. The next level is merely for training purposes before heading to Egypt.
 * Dragon Age: It seems like this is going to happen in the first hour or two. You're told that the Ferelden army has already won two major battles against the darkspawn and are going to finish them off when they come again tonight. Then, when the battle actually STARTS, after you and Alistair complete your mission,, which is how the real game starts off.
 * Dragon Quest VI has a kind task you to slay a dragon deep within a dungeon. When you get there, though, you find that Ineffectual Loner Terry subverts the "Ineffectual" part of his trope and defeats the dragon single-handedly. He then proceeds back to the king to obtain the awesome sword that was promised as a reward, making the whole thing a complete waste of time for you, if only it weren't necessary to advance the plot.
 * Later on, this has a nice reversal:
 * In the second Drakensang installment, you need to solve some ancient puzzles. Going around, you find, that one has already been solved - by a party of Amazons, whom you now have to fight for your MacGuffin.
 * In Dynamite Headdy, the boss of the fourth "scene" has been destroyed before you even get there.
 * Final Fantasy IV. At the bottom of The Very Definitely Final Dungeon, two powerful NPCs destroy The Man Behind the Man you've been planning to kill. At least you get to fight his hatred given form.
 * In Final Fantasy V, Exdeath sends monsters from the Void to stop the party from collecting the remaining tablets. One of them gets killed by Leviathan before he can attack the party, although Leviathan fights you in his place.
 * Final Fantasy VII involves the party breaking out the the Evil Government Headquarters about 5 hours in. However, the door is open and the dozen-or-eighteen guards between you and freedom are already devoid of life. Being the bright intellectuals they are however, the party goes deeper into the building instead of taking the time to leave. This, of course, is to find out who had Already Done It For Them. Spoiler: Ok, maybe not so much a spoiler really...
 * Later, the party has to destroy the gigantic monster simply known as WEAPON. Good thing that Evil Government Headquarters sees it as a threat too, huh? Nothing like a to help the good guys out.
 * In Final Fantasy VIII, as part of a mission to kidnap the President of Galbadia with an unlikely plan involving switching train carriages around, you're told several times how to avoid detection by the train's red and blue sensors (one detects motion, the other heat, and to avoid being detected by them you have to stay still or constantly move when they're on, respectively). When you get to the part of the train with them, you find they're all broken and you can safely ignore everything you've been told about them.
 * Gradius V requires the firepower of another Vic Viper to defeat the final boss. He finishes it off after you destroy your assigned part and leave. You also see him fighting alongside you in his own isolated section of stage 2.
 * One quest in Guardian's Crusade requires you to destroy the Winged Lion monster in order to get the Kuldo Emerald. After battling your way through the dungeon, you find the lion has already been defeated and the emerald harvested.
 * But then if you examine the lion, he gets up to fight again, and you have to defeat him anyway.
 * In Halo 3, you have to take out three shield generators on the level The Covenant. After deactivating the first one, the second is brought down by the Arbiter.
 * In Hitman Contracts, the first level starts with you strolling through a room of Agent 48s that have already been killed. Justified in that you killed them in the original Hitman, and Contracts takes place directly afterwards.
 * In Hyperdimension Neptunia, when Neptune and her friends take on a lost child quest in Lastation, they reach the final room only to discover that has already killed the monster and saved the child.
 * In The Legend of Zelda Ocarina of Time you are told you need to collect six medallions, which is to say five since the quest giver gives you one to start off.
 * The Legend of Zelda: Twilight Princess does this in the final dungeon: As Link approaches the tower where the Master Key is being held, he gets attacked by some Mooks, but several secondary characters arrive and deal with them from the grounds. Admittedly, they were just a few small mooks Link could have easily taken care of anyways, but, still, it was nice to see some Hylians finally doing something to protect their country instead of just leaving everything in the hands of a green-garbed teenager, like they usually do.
 * "Easily taken care of"?! This happened during a cutscene! How do you expect Link to handle a team of trained mooks during a CUTSCENE?!
 * Fate's story path in Magical Girl Lyrical Nanoha A's Portable: The Battle of Aces has Material-S, Nanoha's Evil Twin, telling Fate that there are more Materials like her with her dying breath. As Fate gets ready to hunt down the remaining Materials, Reinforce Eins contacts her with the news that the troubling activities of this incident had finally ceased with her victory. Fate gets confused for a moment about how that's possible, until Nanoha contacts her too and informs her that she had already defeated the other Materials.
 * Then again, Fate's work isn't quite finished yet, as she has yet to defeat the rest of the Dark Pieces and a copy of herself before the incident can be resolved. This trope comes into play in the other characters' routes, as any Dark Pieces or Materials you do not encounter have already been destroyed by one of the other characters you aren't playing as.
 * The first room of Metal Gear Solid has Solid Snake hiding from guards while waiting for an elevator. The "Plant" chapter of Metal Gear Solid 2 opens with another room where you must wait for an elevator, but in a post-modern twist, has already knocked out the guards.
 * Somewhat annoyingly averted in Sonic Adventure. With the Rashomon Style story structure, everyone puts themselves in the spotlight, which means that every time a character is present during a boss' intro cutscene, that has character HAS to fight that boss, even if you've already defeated that boss in another character's story. One of the biggest examples is Chaos 4. Since Sonic, Tails and Knuckles witness its creation, you have to fight him once for each of their stories.
 * One popular fan theory suggests a very subtle example of this trope: During Sonic's Sky Deck level, the Egg Carrier's deck is be reoriented while Sonic goes through to the end of the level. However, during Knuckles' run through the level, he flips multiple switches and reorients the Sky Deck himself, and the theory is that it's Knuckles who causes the changes during Sonic's Sky Deck level, meaning that the level shifts required for Sonic to get through the level are already done for him.
 * The closest the game gets to this trope is in the crossover of Tails' and Big's stories. Froggy wanders into the depths of the desert, and Big would've no doubt found him and be forced to trek through the entire Sand Hill to catch him. However, Tails notices him first and catches the frog, saving Big the trouble.
 * In Metroid Prime 2, the Sky Temple in the dark world requires 10 keys to unlock. The first key was already found and put in place by a dead Luminoth warrior laying at the bottom of the key pillar, leaving only 9 for you to find.
 * In Metroid Prime 3, on the first planet, you are charged with the task of getting 3 generators back online. After you take care of the first one, Rundas, a friendly bounty hunter, sends you a transmission informing you that he took care of the second one and that you should go for the third. He did state he was going after that one before you even started, but, given that side characters in these games, whatever they may say, are generally woefully incompetent at solving any problems big enough for the player to handle, it was a bit unexpected that he actually succeeded.
 * In Super Metroid, you come across several places where the enemies have already, including what appears to be the final miniboss, a golden Torizo statue.
 * Monster Party for the NES. One of the first bosses informs you that he's already dead before you can fight him. Strangely, the one boss in the game that's definitely dead (fried shrimp stuck on a skewer) has no trouble attacking you!
 * In Neverwinter Nights 2 the player must collect five blessings/abilities from five Illefarn statues, and successfully collects 4, only to find that someone else (who later turns out to be a character who has, up until that point, been a villain) has collected the fifth.
 * No More Heroes. As you prepare to fight
 * Fortunately, you get to make up for it in the end,
 * In the sequel,.
 * Also, the Rank 6 battle.
 * In the sequel, there's the rank
 * In Okami, Waka restores the Guardian Tree in ) for you. Between the fact you get Praise for the ones you restore and how obnoxious Waka is anyway, it's easy to forget it's a scripted event and get ticked off at him for it. You can still get Praise from the tree, however, but it requires an alternate method.
 * There was one part in Pokémon Gold and Silver where you team up with Lance to fight Team Rocket and take down their radio broadcast. He takes the left side and you take the right.
 * Mixed up a bit in Pokémon Diamond and Pearl, where after the sixth badge is obtained,
 * In HeartGold and SoulSilver, Victory Road The reason for this?
 * In Rayman 2, after flying a pirate ship and saving Globox's babies, one of the babies reveals that he's stolen the fourth and final Mask. The other three were hidden at the bottom of difficult dungeons.
 * This is different in the remake Rayman Revolution where you have to get the last mask the hard way. The Globox Baby gives you the Rain Mask instead.
 * Resident Evil Outbreak is an instance when this trope is actually a welcome in-game element. The final level of the first game is huge, and requires you to find and combine two key items located in two different areas of the level. You can choose which area you wish to visit first, and nine times out of ten, you'll return to the main building to find that one of your AI partners has already visited the other area and retrieved the second item for you.
 * Happens in Samurai Shodown IV if you don't reach the boss in the time given.
 * In Tales of Symphonia, it turns out that Kratos has already done much of the legwork required to obtain the materials for, leaving only the aionis by the time.
 * In Skies of Arcadia, the fourth Gigas you have to fight for a MacGuffin has already been defeated by the time you finish that dungeon.
 * Ironically, Plergoth was a Chekhov's Gun that the player expected to fight at some point while the others were more or less just Giant Space Fleas From Nowhere who popped up just to fight you.
 * In one level of the Stargate game (for the Genesis), O'Neill had to run around Ra's pyramid destroying all the computer consoles, because one of them was supposed to be special for some reason. When you reach the end of the level, you find Daniel Jackson, who tells you he's already taken care of the right one. He then sends you to kill Anubis (no, not that one) and Ra.
 * Super Mario Galaxy has Luigi searching for stars on his own. Unfortunately, you still need to help him get back to the Observatory, and he gives up after 3 stars, but still.
 * The original Tomb Raider does it deliciously with Pierre - you follow him through, what, four levels, solving every kind of obscure puzzle to open doors, frequently involving destroying permanent fixtures, and then it turns out that he's already there to claim the MacGuffin even though you did all the stuff. How did he get there!? Who knows! Of course, he's the same guy who can ninja-teleport around at will, so, ehehe...
 * The remake turns this around: Pierre, rather sensibly, decides to let Lara risk life and limb pulling every damn lever and switch that's in the way of them and their prize, before waltzing in at the very end to claim it.
 * Except that he still taunts you from areas that are impossible to access without solving various puzzles, and somehow manages to get ahead of you when there's only one way further.
 * Played straight in Treasure of the Rudras be careful of certain actions that may nerf you out of the best equipment
 * Wizardry: Tale of the Forsaken Land gives an example of this that's also a Guide Dang It moment. An NPC wants an item you have absolutely no way of getting yet. To get it you have to basically clear the entire level in one shot as the recipe is pretty far in, and so is the shortcut back to town. You have to do this to avoid level 3, because if you set foot there an annoying NPC will be waiting and make you play a minigame with them. Winning the minigame gets you the item... but also makes them appear on level 5, where they already did it for you, thereby preventing you from getting the nice reward.
 * The World Ends With You is supposed to have quite a few Players also solving the puzzles with you (most of them just seem to be morons who can't even kill the standard Noise). If any Player succeeds at the missions each day, however, any and all survivors will still go on to the next round (this may or may not apply to missions with no time limit). This is surprisingly used twice in the game for plot-related effect, first when, and later when Neku loses in Tin Pin Slammer (the objective was to claim the Tin Pin Golem via tourney), but two other Players win it instead , and once just to Handwave something (a wall is up when approached one way, but down going the other way).
 * Also in the endgame area, you find
 * Justified, in that the person who did it was
 * World in Conflict does this quite often. In one mission, you actually have to help an ally getting some objectives because you have no ground forces to do it yourself.

Webcomics
"Kevyn: If I pee far, it's because I stand on the shoulders of giants."
 * At the end of Eight Bit Theater, The final (fully drawn) epilogue strip has
 * In Schlock Mercenary Kevyn Andreyasn invented a new Faster-Than-Light Travel technology. When one young roboticist shared with him rather idealistic views on how mad scientists should do things out of nowhere and listed the sources, he chose to misquote Newton a little:

Real Life

 * This is vital to the progression of modern science. If undergraduate students did not find out during the first few semesters about how someone had already thought up Linear Algebra, Newtonian Mechanics and Mergesort they would have the opportunity of making fundamental discoveries for themselves—but progress would grind to a halt.
 * "If I have seen far, it is only by standing on the shoulders of giants." Newton was talking about this trope... and giving a Take That to a dwarfish rival.