Are You Sure You Want to Do That?

A phrase said by one character as a subtle warning to another character that their next proposed action is likely to be a big mistake. Trope Namer is Atticus Finch of To Kill a Mockingbird.

It doesn't have to be those exact words. Any question of this type that is on the surface a neutral call for confirmation but is loaded with implied danger if the speaker gets the answer wrong falls under this trope. The speaker is giving whoever is about to make the error a chance to back away from the edge of a precipice before they plummet over into the abyss.

Being asked this is a red flag that you are dealing with a Trickster. If you're being asked it while under said trickster's wing, that makes the character a Trickster Mentor as well, the kind of mentor who prefers to let his or her students make their own mistakes and naturally smooth out the rough edges before teaching them the final touches... but they can't help themselves from issuing a subtle warning that they know that the bold or the chronically indecisive are ultimately going to ignore. (It's fun to watch them fluster over the choice before getting it wrong anyway after all, and a mentor has to have fun, right?) It's also the favorite disclaimer of the Literal Genie.

Of course, this may be used in a serious context later on when addressed to a villain who is about to make his own grave, ruin his own plan, or otherwise screw things up for team evil. This may also be used as a Call Back to the original question to the hero under tuition; all the more appropriate if the question comes from the student themselves. After once being played straight, it is sometimes used as a bluff to unnerve an opponent from making a good move.

Comic Books

 * In the Lucifer one-shot "Nirvana," the title character visits the demon Beruchapalimon for leads about the Silk Man's recent attack on himself. The demon assumes Lucifer intends to read his entrails for clues and so has his Mooks attempt to restrain him while he prepares a magical assault. Lucifer says, "A threat display, demon? Have you thought this through?" Beruchapalimon doesn't take the hint, and proceeds to cast knives at him out of thin air, only for Lucifer effortlessly to turn the knives on the mooks. "I really was just looking for information," he tells the demon, holding a knife to his throat.

Film
"Jack Sparrow: You don't want to be doing that. Barbossa: ...no, I really think I do."
 * In Hot Fuzz, By-The-Book Cop Nicholas asks a culprit whether fighting him is what he "really, really wants". After confirming it, he quips "Suit yourself" and kicks his ass.
 * In War Games, David Lightman logs on to the computer Joshua as Stephen Falken, who in his past liked to research war games. Joshua asks "Falken" if he would like to play a game, and David types in: "Love to. How about Global Thermonuclear War?" Joshua replies, "Wouldn't you prefer a nice game of chess?" As we learn later, the real Falken would prefer chess, but David insists on playing Global Thermonuclear War.
 * In the first Pirates of the Caribbean movie, when Barbossa is about to slit Will's throat and undo the curse:

"Lucius Fox: "Let Me Get This Straight.... You think that your client -- one of the wealthiest, most influential men in the world -- is secretly a vigilante, who spends his nights beating criminals to a pulp with his bare hands... and your plan is to blackmail this person? Good luck.""
 * From The Dark Knight:

Literature

 * Trope Namer is Atticus Finch of To Kill a Mockingbird as mentioned above. He uses it several times in Scout's earlier years before the story as a warning during chess matches that she was about to make a mistake: Scout never took the warning and always got trounced when she ignored it. The second time uses it for drama in a climactic moment that displays Atticus's bravery as he faces down a lynch mob, and, after asking them what they are here for, asks the titular question. It is not this that disperses the crowd however...
 * Near the end of Solo Command, is offered a new identity and a half-million credits in exchange for information regarding certain brainwashing projects that Warlord Zsinj is undertaking. After accepting the deal, she is asked by her liaison (Nawara Ven) whether she wants New Republic credits or Imperial credits. She chooses Imperial credits. After a bit more discussion, Ven gives her one last chance to change her mind, and to work directly for the New Republic. She blows it off...

Live Action Television
"Korax: That saggy old rust bucket is designed like a garbage scow. Half the quadrant knows it. That's why they're learning to speak Klingonese. Scotty: Laddy, don't you think you should rephrase that? Korax: With Scottish accent You're right. I should. Drops accent I didn't mean to say that the Enterprise should be hauling garbage. I meant to say that it should be hauled away as garbage!"
 * Star Trek the Original Series, "The Trouble with Tribbles:"

"Drew: "Paris...Amsterdam...umm...let's do uhh...P...Am...Amsterdam..." (Ryan, Colin, and Wayne all give Drew bemused, questioning looks) Ryan: "Ooookaay!" Drew: "...Let's do Paris.""
 * Bob Barker did this occasionally on The Price Is Right, if someone made a really bad bid, such as $250,000 on a daytime showcase.
 * Happened on ''Whose Line Is It Anyway? during a game of "Greatest Hits". Drew asked the audience for a European city you would go to to have a good time, and got back Paris and Amsterdam and had to make a decision.

Tabletop RPG

 * Classic Traveller supplement The Traveller Adventure. If the PCs decide to get rid of the anolas, the game master is advised to ask them if they really want to do that. This represents the slight but growing hold the anolas have on the PCs' minds.
 * Many RPGs allow characters to acquire a trait called "common sense" (intended for use by players who lack the trait), which obligates the game master to ask this very question from time to time.

Video Games

 * In Apollo Justice, Gavin asks  if he really wants to embarrass himself with . It seems at the time to be simply arrogant taunting, and  does it anyway.
 * In Fallout: New Vegas this occurs upon first meeting Benny where, but only if the player is willing to confirm the action through around a dozen utterances of this trope by Benny. Some of the dialog gets a bit creepy.

Web Comics

 * Order of the Stick: in response to Roy's question here
 * In Collar 6, Butterfly asks this, when the latter confronts her.

Web Original

 * Simmons tries to keep it as non-objective as possible: "Sir, wouldn't it be better if we didn't do that, instead of doing it?" As usually, he is ignored.

Real Life

 * If your Game Master says this in a Tabletop RPG, then you really might want to reconsider your chosen action.
 * Accordingly, a common subject of demotivators.
 * A well designed (modern) computer program will do this before a action that is hard/impossible to reverse, or just plain dangerous/destructive, as a way to make sure you don't accidentally perform said action. Given that computers are the embodiment of a Literal Genie, this is a good thing.
 * Depending on how often this is encountered, people would get annoyed by this to the point of disabling it. Even if it meant your computer was now open to being destroyed by users being stupid.
 * A rather grim example: Israeli PM Yitskhak Rabin refused to wear a bullet-proof vest for the pro-Oslo treaties rally on Nov. 4th, 1995. It cost him his life.