Point of no return
The point of no return is the point beyond which one must continue on one's current course of action because turning back is physically impossible, prohibitively expensive or dangerous. A particular irreversible action (e.g., setting off an explosion or signing a contract) can be a point of no return, but the point of no return can also be a calculated point during a continuous action (such as in aviation).
Origins and spread of the expression
The term PNR—"point of no return," more often referred to by pilots as the "Radius of Action formula" — originated, according to the Oxford English Dictionary, as a technical term in air navigation to refer to the point on a flight at which, due to fuel consumption, a plane is no longer capable of returning to the airfield from which it took off.
The first major metaphorical use of the term in popular culture was in the 1947 novel Point of No Return by John P. Marquand. It inspired a 1951 Broadway play of the same name by Paul Osborn. The novel and play concerned a pivotal moment in the life of an American banker, but they also explicitly referenced how the original expression was used in World War II aviation.
There are a number of phrases with similar or related meaning:
The Point of Safe Return (PSR) is the last point on a route at which it is possible to return to the departure airfield with the required fuel reserves still available in the tanks. Continuing past the PSR, one is now committed to landing at your destination.
- "Beyond a certain point there is no return. This point has to be reached." This statement appears in Betrachtungen über Sünde, Leid, Hoffnung und den wahren Weg ("Reflections on Sin, Suffering, Hope and the True Way") by Franz Kafka.
- "Crossing the Rubicon" is a metaphor for deliberately proceeding past a point of no return. The phrase originates with Julius Caesar's seizure of power in the Roman Republic in 49 BC. Roman generals were strictly forbidden from bringing their troops into the home territory of the Republic in Italy. On 10 January, Caesar led his army across the Rubicon River, crossing from the province of Cisalpine Gaul into Italy. After this, if he did not triumph, he would be executed. Therefore the term "the Rubicon" is used as a synonym to the "point of no return".
- "Alea iacta est" ("The die is cast"), which is reportedly what Caesar said at the crossing of the Rubicon. This metaphor comes from gambling with dice: once the die or dice have been thrown, all bets are irrevocable, even before the dice have come to rest.
The following expressions also express the idea of a point of no return.
- Burn one's bridges This expression is derived from the idea of burning down a bridge after crossing it during a military campaign, leaving no choice but to continue the march. Figuratively, it means to commit oneself to a particular course of action by making an alternative course impossible. It is most often used in reference to deliberately alienating persons or institutions whose cooperation is required for some action. For instance, "On my last day at my old job, I told my boss what I really think about the company. I guess I burned my bridges."
- Burn one's boats. This is a variation of "burning one's bridges", and alludes to certain famous incidents where a commander, having landed in a hostile country, ordered his men to destroy their ships, so that they would have to conquer the country or be killed.
- One such incident was in 711 AD, when Muslim forces invaded the Iberian Peninsula. The commander, Tariq ibn Ziyad, ordered his ships to be burned.
- Another such incident was in 1519 AD, during the Spanish conquest of Mexico. Hernán Cortés, the Spanish commander, scuttled his ships, so that his men would have to conquer or die.
- A third such incident occurred after the Bounty mutineers reached Pitcairn Island.
- Two similar stratagems were used during the Chu–Han Contention (206–202 BCE); these have led to Chinese idioms, elaborated below.
- Also mentioned in the Roman myth of Aeneas, who burned his boats after conquering territory in Italy.
- Similar incidence was recorded in Burmese history. In the Battle of Naung Yo during the attack on Pegu (Prome) in 1540, the Burmese Prince Bayinnaung ( general and brother-in-law of Burmese King Tabinshwehti) faced a superior force of Mons on the other side of a river. After crossing the river on a Pontoon bridge (rafts in another version) Bayinnaung ordered the bridge to be destroyed. This action was taken to spur his troops forward in battle and provide a clear signal that there would be no retreat. 
- "Break the kettles and sink the boats (破釜沉舟)". This is an ancient Chinese saying, which refers to Xiang Yu's order at the Battle of Julu (207 BC); by fording a river and destroying all means of re-crossing it, he committed his army to a struggle to the end with the Qin and eventually achieved victory.
- "Fighting a battle with one's back facing a river" (背水一戰). A similar saying from the same period, which originated in Han Xin's order at the Battle of Jingxing (204 BCE)
- Fait accompli ("accomplished deed", from the verb "faire", to do), a term of French origin denoting an irreversible deed, a done deal.
- Harvey, 1925, 154-155; U Kala II p. 173, ch. 168