That's What I Would Do

"Riddick: Don't bother. Guards ain't there. They figured out the Necros are comin' for me. Plan was to clean the bank, ghost the mercs, break wide for the tunnel. And then somebody got a lucky shot off with this rocket launcher here...and took out the sled. Guards took off on foot, but rigged the door so no one could follow. They'll take the one ship in the hangar and leave everyone else to die. Toombs: How come you know all this shit? You weren't even here. Riddick: 'Cause it was my plan."

- The Chronicles of Riddick

In a story where the villain is a Worthy Opponent, or if the hero and the villain are Not So Different, sometimes it's easy for the hero to predict their antagonist's every move. His Sidekick asks him how he knows what the Big Bad is going to do next, and the hero responds by saying it's because he knows that if their positions were reversed, that's exactly what he would have done.

This is often used to show that the hero and the villain do in fact have more in common than the hero is usually willing to admit, or that they're on the same level intellectually. The line is most often uttered by Anti Heroes or reformed villains who know the tricks of the trade and are able to think like a villain. In Darker and Edgier stories this may push the hero into morally gray territory, letting the audience know that this character who they thought was a good guy may be no better than the villain himself. He doesn't blame the villain for kicking his dog, running over his little sister and devouring that orphanage full of babies, because placed in his antagonist's situation, he would have done the same thing.

In speculative fiction stories, sometimes the hero knows what the villain will do because they may be effectively the same person, in which case it is much easier for the hero to imagine himself in the villain's shoes.

Sometimes this line is uttered by the villain himself, who understands the implications of his actions and realizes that the hero is only doing his job, and tells the hero that he doesn't hold it against him for trying to kill him, and he should just get it over with, either because the villain knows that if he were the hero he would do the same, or because the villain wants the hero to know that he's just that much of a bastard and would be just as likely to kill the hero if he were given the chance. It's also a common line of The Atoner, particularly if he or she is protecting someone from his or her former kind (such as Career Killers). Of course, kinder and gentler heroes will not take the villain up on his offer in order to show that there is, in fact, a difference between them and that the hero will not stoop to the level of a villain by obliging his request.

Anime and Manga
""STRAAANGE isn't it?!""
 * Shishio, the Big Bad of the Kyoto Arc in Rurouni Kenshin, wonders out loud if this is the reason Kenshin figured out his nefarious plot so quickly.
 * L and Light of Death Note. All the time. Heck, L says as much in the first episode we actually see his face!
 * Sonic and Hyper Metal Sonic in the two-episode Sonic the Hedgehog OVA.

Comic Books

 * In the Batman series Knightfall, the Batmobile is stolen. Batman gets it back, starts the car...and it explodes. Fortunately, he guesses this just in time to leap out of the car. Robin asks him how he guessed the villain had wired the car to blow. Batman's response: "Because that's what I'd do."
 * In The League of Extraordinary Gentlemen, this is how Moriarty knows that Holmes will try to fake his death after their encounter at Reichenbach Falls.

Fan Works
"A memory of awful clarity came over Frodo then, and a flash of black laughter, and the thought came to him that it was just what the Enemy would do. Only the thought came to him so: thus it would amuse me to do, if I meant to rule..."
 * In some Omake in Harry Potter and the Methods of Rationality, titled Lord of the Rationality, Frodo thinks:

Film
"John Connor: I gotta stop by my house. I wanna pick up some stuff. T-800: Negative. The T-1000 would definitely try to reacquire you there. John: You sure? T-800: I would."
 * Terminator 2: Judgment Day


 * Variation in The Fast and the Furious: Brian tries to narrow down a list of suspects with the same name to figure out which one is involved with street racing. He has his FBI partner read off a list of the suspects' cars. After hearing about a Nissan 240SX with an illegal modification, he remarks that he's the one. His partner asks how he knows this and he replies "Because that's what I'd drive."
 * In Chronicles of Riddick, Riddick seems to know everything that happened in the fight that he wasn't there to witness, and then the others escaped in the chaos. When asked how he knew all that, he said it was his plan.
 * In Saving Private Ryan The Squad comes under attack by a sniper in a French village. The squad's sharpshooter Jackson spots a tall church tower and says, "That's where I'd be".
 * In Predators, being a veteran hunter himself, Royce mentioned in detail how the predators would approach in killing their prey, quoted this exact line "that's what I would do".

Literature
""You see, I had murdered them all myself.... I had planned out each of the crimes very carefully. I had thought out exactly how a thing like that could be done, and in what style or state of mind a man could really do it. And when I was quite sure that I felt exactly like the murderer myself, of course I knew who he was.""
 * In Neil Gaiman's short story A Study in Emerald, a crossover between Sherlock Holmes and H.P. Lovecraft, the detective tells the narrator that he figured out how the murderers got away based on the fact that he would have done the same thing. The twist is that.
 * Father Brown, of the eponymous stories by G. K. Chesterton, solves all of his mysteries this way. His gimmick is that, as a priest and confessor, he knows a great deal about how crimes are committed and what kind of people commits them.


 * Sherlock Holmes claims to be using the same method. In one of the short stories, Holmes matches his wits against an unusually clever criminal (no, not Moriarty). Afterwards, he tells Watson it was one of his easier cases; normally he has to adjust his deduction of what the criminal would do, since most people are significantly less smart than himself, Holmes. But in this case, what the criminal did is exactly what Holmes himself would have done, making it easier for Holmes to follow him!
 * The Quiller novel The Ninth Directive has Quiller tasked to plan the assassination of a "Very Important Royal Person" with the intent that this will show him exactly how the real assassin plans to do it.

Live Action TV

 * In Heroes, Nathan cites his belief that the government would capture and experiment on anybody with powers as exactly what he would do in the situation.
 * In season one of Lost, Sawyer, after being stabbed by Sayid, tells Jack that he should just let him die, saying that he knows it's what Jack wants to do and that he would do the same to Jack if he were in his shoes. Of course, Jack saves him anyway.
 * Cameron uses this to predict the actions of enemy Terminators in The Sarah Connor Chronicles.
 * Possibly a call back to the T2 example mentioned above.
 * There's a scene in Babylon 5 where Sheridan predicts a particular move by the Shadows because "that's just what I'd do." Delenn is horrified by the notion of Sheridan thinking like the enemy.
 * There's an episode of Criminal Minds that pretty much epitomizes this trope, "Elephant's Memory". Spencer Reid has insight on the case because he identifies with the unsub, as they shared a history of being bullied in school. At one point he uses this exact phrase when asked how he.
 * As a white collar criminal hired to catch white collar criminals, Neal Caffrey of White Collar makes good use of this trope. He frequently deduces how criminals must have hidden their tracks by thinking over how he'd do it.
 * In the Star Trek episode "Balance of Terror", this is Kirk's comment after the nameless Romulan commander dodges one of the Enterprise's attacks: "He did exactly what I would have done. I won't underestimate him again."
 * Stargate SG-1: This is how the real SG-1 bests the evil, alternate universe team in "Ripple Effect." Of course, they had the added advantage of being basically the same people as their opponents.
 * The Doctor Who two-parter "The Rebel Flesh"/"The Almost People" has a lot of this, since all the one-off characters—and the Doctor—get duplicated throughout the course of the story. Most impressively, one of the doppelgangers manages to guess a password that her original created after the split happened, because it's the password she would have used.
 * The Doctor Who two-parter "The Rebel Flesh"/"The Almost People" has a lot of this, since all the one-off characters—and the Doctor—get duplicated throughout the course of the story. Most impressively, one of the doppelgangers manages to guess a password that her original created after the split happened, because it's the password she would have used.

Video Games
"Lara Croft: "What the hell are you?" Doppelganger: "" Lara: "If you were your own master, what would you do?" Doppelganger: """
 * At the end of the Lara's Shadow Downloadable Content for Tomb Raider: Underworld, Lara confronts her doppelganger after gaining control of it.



Web Original
"Cassidy: Keep on the lookout for anybody in the crowd just trying to blend in, but seems to be doing more. Particularly if they are keeping an eye out for Narcissa or scanning around. It's just a hunch, but I suspect she may have assistance hidden within the crowd. Wynn: No prob. Only thing I ask to know is why you think that? Cassidy: Because that's what I'd do."
 * Grandmaster of Theft this usage:

Real Life

 * Generals often predict the each other's plans when the required intelligence isn't available in this manner. This approach can backfire horribly if the predicting general failed to understand his opponent is more ruthless then he is, or when the enemy has access to information the predicting general doesn't know exists.
 * Some generals also take this one step further. They knew their enemy will try to predict their actions in this manner, and therefore alter their plan accordingly.
 * This can lead to some pretty interesting battles. For instance, during WWII the Germans thought the invasion of Normandy was a diversionary attack while the assault on Pas-de-Calais (which is geographically closer to the British Isles and therefore the more reasonable target) was the real push; in reality, the situation was reversed. The Allies were perfectly aware the Germans had predicted they would strike Pas-de-Calais, so they encouraged that line of thought with a massive misdirection campaign and struck elsewhere.
 * Frank Abagnale of Catch Me If You Can, his autobiographical book and movie. Eventually, he ends up working with the government tracking down conmen like himself. The few scenes you see of him doing this in the movie include him making similar remarks to the trope name.