This Is as Far as I Go

A Stock Phrase usually used by a guide or mentor. After traveling with The Hero up until a certain point, they have to stay behind from there. Perhaps because they aren't the Chosen One or because they're no longer allowed to after what happened the last time. It's may also be that as a gatekeeper, they must stay back to guide travelers or protect their home. Of course, it's also possible that they're just a jerk or a coward and don't want to go.

A common trope, as it gives a quick excuse for why powerful characters can no longer follow The Hero. Can often be used as a set up for a Big Damn Heroes moment.

Anime

 * In one Ghost in the Shell: Stand Alone Complex 2nd Gig episode, Togusa and a woman are looking for a man in a refugee city. They happen upon a teenage who worked with the man in a coal mine and owes his life to him for getting him out in time before the mines were sealed shut after an incident, with many workers trapped inside. When asked if he would take them to the mine entrance, the teenager initially refuses. But after some prodding, reluctantly leads the two there before stating he won't go any further.

Comics

 * In Return to Plain Awful, Flintheart Glomgold hired a guide to take him to the village of Plain Awful. When they reached a wall they could easily jump, the guide invoked the trope. Assuming the guide was just being cowardly and/or superstitious, Glomgold jumped the wall before the guide had the chance to explain why they shouldn't go further. Glomgold jumped off a cliff.

Film
"Goblin: Here we are... and there they are. Seventy times seventy soldiers. Sometimes I wish we'd never created them. Bim-bam went the hammers! Whoosh went the furnaces! One of those fires took my legs off. This is as far as I go. I'm not very good with steps. But if you're here to stop him, the Prince, I wish you luck. The Golden Army must not awaken. Undo what we did."
 * Very common in old horror films, particularly the various versions of Frankenstein. The protagonist would ask for a ride to the Mad Scientist's castle, and whatever frightened villager would be foolhardy enough to oblige would stop at the long road up to the castle, then explain that "I can take you this far and no further."
 * Hellboy II: The Golden Army

"Coleman: Here's a little bon voyage present for you guys. Gunpowder, nitroglycerine and .44 caliber primers. Gordon: How the devil do you know about explosives? Coleman: U.S. Marshal Coleman. The President wanted me to look after you. But I draw the line at defying gravity, so good luck."
 * A variant in Wild Wild West. Coleman (the engineer of the protagonists' train) has been with them through several encounters with Loveless' forces. Now the heroes are about to take to the air in a primitive flying machine.

"Aragorn: (to Frodo) I would have gone with you to the end. Into the very fires of Mordor. Frodo: I know."
 * Inverted in the film version of The Lord of the Rings: Fellowship of the Ring when The Hero, Frodo, chooses to go on alone into Mordor, although his far more experienced companions would willingly have gone with him.


 * In Clockstoppers, Zack Gibbs enlists the help of Dr. Earl Dopler to rescue his dad from Quantum Tech. But when they reach the organization's headquarters, Dopler refuses to go any farther. He claims he is too traumatized by his previous imprisonment at QT to go back. But he apparently has a change of heart, as he reappears in the ending to help out at a critical point.
 * In Mighty Morphin Power Rangers The Movie, the rangers went to another planet to seek the power to defeat Ivan Ooze. There, they met a warrior who agreed to guide them around but reached a spot where she said she'd grow older than Zordon if she ever went further.

Live Action TV

 * Lampshaded in The Mighty Boosh episode Jungle. After Howard passes the test to prove his worth to Rudi, Rudi agrees to take him part of the way to the centre of the jungle. Rudi carries Howard forward about two metres before claiming it's as far as he goes.
 * Played with a bit in an episode of Boy Meets World. When stuck in Amish Country, Corey's trying to walk back home, when he's lapped by an amish man in a buggy. The man offers Corey a ride, but informs him he's only going as far as "that barn, there", somewhere nearby offscreen. Corey remarks on how useless the offer is.
 * In the two-part first episode of Pair of Kings, the Kings got help from the Tarantula people to get a new ruby. The Tarantula people refused to enter the temple, which surprised the Kings, considering everything else the Tarantula people agreed to do. However, given the dangers inside the temple, the Tarantula people were justified in their refusal.
 * Gwaine does this in season 3 of Series/Merlin, when he still can't come back to Camelot or Uther will kill him.

Literature

 * Gandalf does this in The Hobbit.
 * In Harry Potter and The Philosopher's Stone, Ron and Hermione stay behind when Harry goes on to face Voldemort. In the movie, it's made explicitly clear that this is because they know he is the Chosen One.
 * In Northern Lights (aka The Golden Compass), Iorek cannot cross the ice bridge, and thus Lyra must go alone to face her father.
 * In Rudyard Kipling's "Red Dog" Kaa the python helps Mowgli in his plan to attack the invading dogs and transports him safely down a raging river, but leaves before the surviving dogs reach Mowgli's wolf pack because it's not his fight.
 * Each of Dante's guides in The Divine Comedy can only go so far with him because of their divine fates. Vergil, his first guide, can only lead him to the end of Purgatory because he's bound to the First Circle of Hell (the "noble pagans") and his forbidden to enter Heaven.

Tabletop RPG

 * Dungeons and Dragons
 * Adventure I2 Tomb of the Lizard King. If the PCs have some mercenary guards accompany them on their journey, the guards will leave them once they reach the village of Waycombe.
 * Adventure OA6 Ronin Challenge. The PC party is escorted on their trip south by a squadron of Imperial cavalry. There is a bad omen and 1/3 of the troops desert. Shortly thereafter the officer in charge tells the PCs that he can accompany them no further and that they're on their own.
 * Call of Cthulhu (tabletop game) supplement Fragments of Fear, adventure "Valley of the Four Shrines". When the party reaches the cave that leads to the Valley, any native porters hired from nearby areas refuse to enter.

Theater
"Madame Giry: This is as far as I dare go, sir."
 * The Phantom of the Opera, as Madame Giry leads Raoul to the Phantom.

Video Games

 * In Final Fantasy VI, Shadow does this a lot. The first several times it's because he's a mercenary who decides to leave you at one point or another. The last time
 * Common Catch Phrase for the cowardly scientists in Half Life.

Western Animation

 * In an episode of Ben 10: Ultimate Alien, Paradox takes the protagonists to the edge of a section of space he's no longer allowed in because of an intergalactic treaty, but leaves before he draws attention to himself.
 * Spoofed on Futurama, "The Honking", where the villager says the phrase at the front door of the castle.
 * In Dexter's Laboratory Ego Trip, Dexter and his 22-year-old future self went further into the future to see the utopia they'll create with their neurotomic stabilizer. A guide showed them the way to the home of an elderly Dexter but wouldn't enter for considering himself unworthy.

Real Life

 * In WWII, the US bombers had a longer range than US fighters. Thus, when they raided Germany, the fighters would escort the bombers, but they'd have to turn back before the bombers reached their targets, leaving the bombers unprotected when they needed it the most.