Most commitments and endeavors are temporary, by nature or design. High school typically takes four years, advanced degrees between two and ten, exploring an unknown region of space might be a five-year mission, democratically-elected representatives typically have term limits, and so on. These things are temporary.
Some things do not have such limits. In fact, some commitments, endeavors, or sentences are explicitly designed to be lifelong. Other times, something that is ostensibly temporary will be extended or renewed in perpetuity, rendering it de facto lifelong. The person who winds up in such a position, therefore, is In It For Life. Note, however, that some things intended to be lifelong commitments (such as marriage) don't always wind up this way, with people managing to end their commitment early.
By definition, the Ur-Example is life itself, which is also the only example which can be universally applied to living things.
Compare Mandatory Unretirement.
- Green Lantern: Red Lanterns can never quit. To avoid people leaving his Lantern Corp, Atrocitus designed the Red Rings so that taking them off would be fatal. Only the healing power of a Blue Lantern can prevent this.
- In the Supergirl crossover Red Daughter of Krypton Supergirl becomes a Red Lantern. In "Red Lanterns #30" -properly titled "Forever"- she finds out that she'll be a Red Lantern forever (and, predictably, she isn't happy about it). Of course, she does not stay a Red Lantern forever.
- Wonder Woman Vol 1: In the Golden Age of Comics those who became an Amazon dedicated the rest of their lives to the Amazons' causes, and those who visited Paradise Island and actually chose to become Amazons also had their lives extended far beyond the normal human timespan.
- The Chronicles of Narnia: "Once a king or queen in Narnia, always a king or queen in Narnia." Important because it is not unknown for children from Earth to be taken to Narnia, installed as king or queen, returned to Earth, and then be returned to Narnia years, decades, or centuries later at which time a new ruler may be in place.
- The Murderbot Diaries: In the galaxy-spanning sci-fi setting, the Corporation Rim is a Privately Owned Society and de facto slave state where it's common for the less fortunate to sign away their labour and personal rights to their "employer" in perpetuity. Many colonies there are isolated Company Towns where the descendants of indentured labourers have no way to escape and no other means of survival.
- The Reynard Cycle: When you become a Calvarian blood-guard, you are considered one until you are dead. Of course, you may die before you get that far.
- In A Song of Ice and Fire, service as a maester, in the Night's Watch, Kingsguard, and several religious orders is lifelong. The Night's Watch' traditional funeral rites end, "Now his watch is ended."
- In The Wheel of Time, service as an Aes Sedai (female magic-user) is intended to be lifelong. When the new Amyrlin Seat (a cross between The Archmage and a female Pope) breaks tradition by demoting an Aes Sedai to Accepted (apprentice), it causes a major scandal. Even when it's discovered that the Restraining Bolt that is a major part of their identity as Aes Sedai shortens their lifespan by several hundred years, there is a significant faction that would rather die as Aes Sedai than "retire" and have their lifespan restored.
- Babylon 5: The Rangers appear to be this, although it's never specifically stated. Their motto is "We live for The One, we die for The One", and beyond that they are all volunteers, self-selecting for their dedication to the cause. The "Die for The One" part does get a bit of stick in the spin-off move Legend Of The Rangers, where the Captain points out that they're not supposed to die stupid - broadly, that today is a good day to not die, and tomorrow is as good a day as any to fight another day.
- Game of Thrones: The Night's Watch's vows (to hold no titles, take no wife, and defend the Wall against northern invaders) are for life. After Jon Snow is murdered and is resurrected, he considers his previous commitment to have ended, and later takes the title of King in the North. At the end of the series, he is sent back to the Night's Watch after killing Daenerys, and will presumably stay there permanently.
- The D-class of the SCP Foundation are used as grunt labor and guinea pigs, taken from death row or third-world prisoners (and in times of shortage, from the general populace) for a promise of a shorter sentence, and are traditionally executed at the end of the month. A life sentence doesn't necessarily imply a long sentence.
- Some entries and stories on the site imply that there are other sources for D-class as well, such as cloning. Yet others imply that the monthly executions are a just a front, and that D-class are mind-wiped or otherwise reset before taking up new (but usually still inconceivably horrible) roles for the next month.
- In the Pacesetter Games version of Chill, all PCs are required to be members of S.A.V.E.. This is enforced by stating that any member of S.A.V.E who is kicked out for breaking the rules will be killed by supernatural monsters within the week, with no way to avoid death.
- Warhammer 40,000:
- Space Marines serve until they die or they are too grievously wounded, at which point they may be put inside a Dreadnought to continue serving pretty much eternally.
- Penal legions are pretty much this, since the idea is to redeem yourself of a particularly hideous crime by going on the most dangerous or suicidal missions.
- Fire Caste warriors either serve until death or face trials every four years of service to go up a rank, at which point they can become advisors.
- Dwarf Slayers are individual dwarfs who have dedicated themselves to dying in battle against a particular enemy (Troll Slayers, Dragon Slayers, Demon Slayers etc.) to atone for some past dishonor. The most successful ones are technically the biggest failures, since they're bad at the "dying in battle" part.
- A human who joins the Imperial Colleges of Magic is bound to their code of conduct for life, not least because they're the only exception to the terminally-enforced Ban on Magic. However, they gain more freedom once they demonstrate their reliability: apprentices-in-perpetuity often hold day jobs and even full magisters sometimes disappear on personal projects, so long as they follow the rules and come when called to active duty.
- The "In For Life" flaw in Mechwarrior (the tabletop roleplaying game, not the video game of the same name). You're part of an organization for good or for ill. Normally, this most often applies to organized criminal groups like The Mafia, Yakuza, or The Triads and the Tongs. It can also apply to things such as elite government organizations, especially all forms of Secret Police.
- In West Side Story, "when you're a Jet you're a Jet all the way, from your first cigarette 'til your last dying day."
- Assassin's Creed: Both Assassins and Templars operate by this, though only the Templars have it as an explicit part of their oath, to serve from joining until death.
- In Mass Effect, there's "no such thing as a former Spectre". The closest you can get is Shepard in Mass Effect 2, as the game starts with them dying and then coming Back from the Dead. You get to choose whether you have your status reinstated or not... until the third game, when it's reinstated anyway.
- Likewise, in Dragon Age, there is no such thing as a former Grey Warden, as the Taint they voluntarily expose themselves to during their Joining ritual is incurable. There is a single known example of a Grey Warden being completely freed from the Taint—Grand Enchanter Fiona—but she was the only success of a centuries-long research by an inhuman intelligence that is yet to be replicated.
- Common for many gangs and other criminal organizations, usually expressed by the phrase "blood in, blood out". You get in either through a Blood Oath and/or by committing a violent crime, but you only get out by dying. For examples, see Resignations Not Accepted.
- Justices of the United States Supreme Court are usually in their positions for life.
- This applies to any federal judge, in fact. Per the US Constitution, judicial appointees "shall hold their Offices during good Behaviour", meaning that the only way for them to leave the bench is by voluntarily retiring, resigning to take another appointment, being impeached and convicted (which has only ever happened 14 times total across every federal judge ever) or dying. This was done to keep the judiciary independent of executive order legislative interference under the separation of powers theory that underlines the constitution, but has also been criticized as leaving people on the bench for far longer than they should reasonably stay.
- Marriage is traditionally this in most cultures. As it is currently practiced in modern Western society, it is averted roughly as often as played straight. Most people still keep the "until death do you part" bit in their vows, although Fridge Logic sets in if one or both spouses have one or more living ex-husbands or -wives. If a couple persists in marriage due to the lifelong commitment involved despite being miserable, it's an Awful Wedded Life.
- "Once a Marine, always a Marine." Largely symbolic as they are not (usually) literally expected to serve for life. Military commitments in general are typically relatively short, with service terms between two and six years being common. While many folks proceed to get out of the military and get another job or go to school, some folks will "re-up", possibly with the intent of serving until they reach retirement age, such folks being known as "Careerists" or "Lifers".
- Most royalty and nobility are this way, with "Dowager" added to the honorific of a widow whose title derives from a deceased husband and whose effective authority has passed to an heir (e.g. "Dowager Countess").
- Many religious orders, such as the Catholic priesthood, are for life. While there is provision in Canon law for popes to resign, it is very rare, making the papacy functionally this. It was most recently averted by Pope Benedict XVI, the first living pope to step down in centuries. And it had been even longer than that since a pope had resigned voluntarily, rather than at the point of a sword. Similarly, once baptized Catholic, always Catholic, at least in the eyes of the Church — no matter what the "fallen sheep" in question might have to say about it. Said "fallen sheep" could convert to Buddhism, abandon organized religion altogether, or turn outright atheist, but as far as the Church as concerned, they're still Catholic.
- Life imprisonment is a common punishment for severe crimes such as murder, especially in jurisdictions that lack the death penalty. See also: Longer-Than-Life Sentence.