A character (possibly with the best of intentions) has started or gotten involved in something which has become dangerous or taken an evil turn, but which they cannot just stop doing or walk away from without facing terrible consequences. This can be a case of either Gone Horribly Wrong or Gone Horribly Right depending on the circumstances. The idiom comes from the idea that if you catch a tiger by the tail, you can never let go unless you want to be eaten. Also known as "riding a tiger" from the Chinese idiom "riding a tiger and unable to get off."
Perhaps the character started a protest movement that has become violently fanatical, and would execute them as a traitor if they tried to mitigate its behavior. Maybe they stumbled into a MacGuffin and the government is now after them until they Clear Their Name, or they jumped into the pilot seat of a Humongous Mecha to repel the alien invasion, only to find It Won't Turn Off, and it becomes such a Murderous Malfunctioning Machine in battle that it would love to try to kill them if they ever try to disembark.
Unlike with I've Come Too Far and Sunk Cost Fallacy, it's not a matter of the character not wanting their efforts or expenses to go to waste. It's that they will die or otherwise suffer terribly if they don't carry on. If a good guy gets into this situation (and the work isn't cynical), there will usually turn out to be a third option, or outside intervention to help him.
See also Godzilla Threshold, which can involve knowingly getting into this; and "Fawlty Towers" Plot and Crime After Crime, which can be this depending on the circumstances (although the former is usually more lighthearted in the stakes). This can sometimes be a Morton's Fork if disaster from stopping or carrying on seems equally inevitable.
- Volume 1 of The League of Extraordinary Gentlemen ends when the Big Bad, Moriarty, impulsively grabs the cavorite after its container has been shattered. The anti-gravity metal shoots into the sky, and Moriarty realizes an instant too late that he's too high up to let go. Moriarty's frozen corpse, still holding the cavorite, shows up in a later volume.
- Jaune finds himself in this situation in A Rabbit Among Wolves. He accidentally kills Adam Taurus, gains control of the White Fang, and becomes a wanted fugitive. Hoping to prove to Remnant he isn't evil, he tries to reform the White Fang enough so he can quit and go back to a normal life. Unfortunately, he succeeds well enough that he goes from being a rising star to an icon. Adam's ghost spells out to him that him quitting would devastate the White Fang, and even send them back on the path toward violence, much to his frustration.
- This is the situation Taylor finds herself in halfway through the second arc of I Am Skitter. She is horrified by what Skitter has done and realizes that this is far beyond what she wanted to happen when she first created Skitter. She further notes that she technically could still stop this, push Skitter back into whatever part of the subconscious she pulled her from in the first place and retake control of her mind. But if she did so, she would lose Skitter's cunning and poise, and without those she doesn't have a hope of staying ahead of the PRT. So she decides that she has no choice but to let Skitter have her head and simply watch the rampage from behind her eyes.
- A version involving a literal tiger occurs in The Jungle Book (1967). Baloo arrives just in time to grab Shere Khan by the tail when he charges at Mowgli. After the vultures have air-lifted Mowgli away, one of them tells Baloo he can release Shere Khan's tail now.
Baloo: Are you kiddin'?! There's teeth in the other end!
- Oscar's getting famous off Frankie's death in Shark Tale spirals into the population wanting him to fight more sharks despite his lack of actual fighting ability, which then spirals into Oscar having to help Lenny fake his death so the latter doesn't tip him off to Don Lino, which leads to Lino kidnapping Angie in revenge for both his sons' deaths. Angie tries to get him to reveal the truth, but Oscar laughs her off since doing so would result in him losing all of his fame, likely being sued and getting eaten by sharks who wouldn't be afraid of him anymore.
- In The Guilty, Rashid doesn't particularly want to keep lying about his partner Asger's killing of a suspect to protect him, but fears what might happen if he were to change his story.
- Guards! Guards!: Lupine Wonse summons a dragon in a plot to usurp control of Ankh-Morpork. When the dragon escapes his control, rather than eating him, it makes him its servant, and he ends up living in constant terror of it, but also in terror of what will happen to him if he tries to escape.
- Men at Arms: An shown in the above quote, when Nobby starts swinging around his Epic Flail, he finds he can't safely stop. Fortunately, Carrot is big enough to safely intervene.
- The gang employed by Teatime in Hogfather refer to "that saying about riding a tiger" as they realise that attempting to leave before the job is finished will slightly increase the likelihood of them all being killed.
- In Going Postal, the Grand Trunk's board of directors eventually realize the true nature of Reacher Gilt. They also realize that Gilt has dirt on all of them thanks to Crispin Horsefry's blabbing; they're not only riding a tiger, but the tiger knows where they live
- In A Song of Ice and Fire, Cersei cynically reinstates the Faith Militant in the hopes that they will find some reason to destroy the Tyrells, whose daughter Margaery is about to marry Cersei's son Tommen and become Queen. The Faith Militant lock up Margaery, but during the course of their investigation, they decide that Cersei is also guilty of various sins, and she is locked up as well, only being released after effectively agreeing to be their puppet.
- Namechecked in After the Revolution by Dr. Brandt, when he explains to Sasha how bad a position the Heavenly Kingdom is in because they took The City of Wheel's envoys prisoner. While holding the three hostage means the powerful cyborgs probably won't attack right now, in the long term this move put the Kingdom in direct conflict with a heavily-armed polity who already hated them on principle.
- The People v. O. J. Simpson: Robert Kardashian finally realizes that O.J. is most likely guilty several months into the trial. He can't leave the defense without destroying his career and guaranteeing a guilty verdict (which would violate due process.)
- In season five of The Walking Dead, the Atlanta Police Department and the surviving doctors of the main hospital have created a system where they "rescue" people but force them into servitude to pay their weight. The leader of the cops, Dawn, seems to realize it's gone too far but can't stop it without risking a mutiny.
- The Trope Namer is Buck Owens' song, "I've Got a Tiger By the Tail."
Well, I thought the day I met you, you were meek as a lambJust the kind to fit my dreams and plansBut now, the pace we're living takes the wind out of my sailsAnd it looks like I've got a tiger by the tailI've got a tiger by the tail, it's plain to seeI won't be much when you get through with meWell, I'm losing weight and turning mighty paleLooks like I've got a tiger by the tail
- Ravenloft: Wyan of Viktal started the Inquisition to combat The Fair Folk and those who conspire with them, but the group has become fanatical over time, and often not really interested in giving the accused due process. Wyan is a good man and not happy about this, but knows he would likely end up burned at the stake if he tries to speak out or leave.
- BioShock Infinite: While Booker is infiltrating Monument Island to rescue Elizabeth, he learns that the rulers of Columbia have expended a great deal of money and effort to imprison her. She has tremendous power they want to control, but are also scared of. He finds a voxophone left by a janitor who works there. Its message explains the dilemma the Columbian leaders are in.
Ty Bradley: But I can tell they scared out of their wits by that thing they got locked upstairs. Yes, sir. They got a tiger by the tail, and they don't know whether to hang on...or run.
- The Elder Scrolls series has an in-universe short story, Sacred Witness, in which the author sets out to learn more about the Night Mother, infamous leader of the Dark Brotherhood assassin's guild. He is eventually granted an audience with her, but in order to prevent him from sharing her secrets, she conscripts him into the Brotherhood and makes him assist them in committing unspeakable crimes. The book ends with the author admitting that the Night Mother will see the book's publication as him breaking his promise to her and that he fears for his life, followed by an editor's note stating the author was found dead with his corpse bearing the Night Mother's Calling Card.
- In Brink, one of Captain Mokoena's diaries talks about "Chen riding a tiger", referencing his belief that his rival Brother Chen has allied with dangerous fanatics for selfish political gain.
- Dragon Age: Inquisition: Mistress Poulin, the ruler of the town of Sahrnia in Emprise du Lion, let the Templars mine her quarry and hire the locals to help. The town was dying due to the Orlesian Civil War and desperately needed the money. She learned too late that they were Red Templars in service to Corypheus and the people she was sending them were being killed in the process of mining the red lyrium. She knew that if she refused to send anyone else to work the quarry, the Red Templars would just attack the town and take everyone at once. She sold the weak, elderly, sick, and anyone else that was likely to die soon anyway. She used the coin to help the survivors and hoped that someone would come along to save them before they all got killed anyway.