It's a powerful magical artifact, unique high-tech gadget or just an extremely valuable prize. As long as the hero can hold on to it, they will be victorious in the end... which is of course why they are constantly dropping it or having it stolen from them. If the item is the source of their power, this will serve to create a frequent Drama-Preserving Handicap by forcing them to solve a problem by themselves that would have been trivially easy if the absence of the item hadn't caused them to be Brought Down to Normal. Either way, both tense scenes and longer plot arcs can be created by the hero desperately trying to get the item back.
Sometimes this is justified with the item being an Empathic Weapon or Artifact of Doom that has a will of its own and either doesn't want to stay with the protagonist or takes a perverse delight in "testing" them by withdrawing its help and seeing how they get by without it. Other times, though, it's just another example of protagonists having the worst possible luck as long as that makes things more exciting.
Another possible variation of the trope is the magical artifact of Game Breaking power that the protagonists need to locate for a single, critical use. Having employed it to resolve their current troubles, they will promptly lose it, which is explained by the item being too magical and mysterious to stay in any one person's hands for too long.
Contrast the Loyal Phlebotinum, which won't abandon you and will actively try to get back to you even if you should lose it anyway, and Clingy MacGuffin, which you can't get rid of no matter how much you might want to. Note that in some cases, whether a MacGuffin is Slippery or Clingy/Loyal depends on your perspective. A talisman that is trying to return to its true owner will be Clingy in regards to that owner, but Slippery to anyone else who tries to hold on to it.
If this trope is sped up to the point where no one can hold on to the object for more than a few seconds, you will end up with a MacGuffin Melee.
Examples of this trope include:
Anime & Manga
- The eponymous wish-granting objects of Dragon Ball scatter across the world after being used (and are completely inactive for up to a year). However, the heroes eventually become so strong that gathering them becomes an unnoteworthy task done off-screen.
- The One Ring in The Lord of the Rings movies wants to return to its true master Sauron, and will subtly influence events to make that happen. In the backstory, it abandoned first Isildur and then Gollum at a critical time. In the movie version of The Two Towers, it also manipulates Frodo into offering it to a Nazgul during the siege of Osgiliath. It is only thanks to Sam's interference that Sauron doesn't get the Ring back.
- The Lord of the Rings: The One Ring is a Slippery MacGuffin to the heroes because it's a Clingy MacGuffin to its evil creator Sauron, and will subtly influence events to bring it back to its master (as characters mention, "it wants to be found" which is why burying it or casting it into the sea won't work). In the backstory, it abandoned first Isildur and then Gollum at a critical time.
- Robert Jordan's novel Conan the Magnificent plays with this trope. The villain's (literal and figurative) Dragon can only be slain by a certain magical sword, which can only be granted to a worthy wielder, and only once in a lifetime. If the true wielder loses the sword, it will eventually find its way back to the sacred grove where it is normally kept, and only then can it be granted to a new wielder. Conan is not the chosen wielder, and so from the moment he picks up the sword he's doomed to lose it - but since by the time he gets his hands on it, he's standing right in front of the dragon, he doesn't actually need to hold on to it for more than the few seconds it takes him to slay the beast.
- Tough Times All Over, a short story set in the world of The First Law, follows a mysterious package as it switches hands repeatedly over the course of a night, time and again getting stolen or passed along like a hot potato, and ultimately ending up in the hands of the same courier who lost it in the first scene.
- The epynomous Witchblade is said to be prone to abandoning its wielder in her time of need, something Sara gets to experience a few times over the course of the series. Flashbacks show that previous wielder Joan of Arc died crying out to it, demanding to know why it had betrayed her.
- Wil Ohmsford in The Shannara Chronicles can't seem to keep hold of the Elfstones for more than five minutes in a row. You'd think he'd at least tie that pouch to his wrist or something.
- The episode "Bad Day at Black Rock" of Supernatural features a magical rabbit's foot that grants incredible luck as long as you have it, but which also curses you with equally bad luck if you lose it. Naturally, part of the enchantment is that you'll always lose it before long.
- The City of Angels supplement for Demon: The Fallen mentions a magical sextant created by the demon Gripontel. It can lead its bearer to any destination, but will often mysteriously disappear after doing so.
- Nethack has the amulet of Yendor. The entire game is about finding it (and offering it to your god). But one of the bosses will do its hardest to reappear and take it from you. Oh, and beware shoddy plastic knockoffs. It would be ever so embarrassing to offer one of those instead.
- In The Elder Scrolls series, the Daedric artifacts fit. They are extremely powerful and legendary magical items (often weapons) that are granted to mortals by their associated Daedric Prince, typically by performing a service for the Prince in question. Given that most of the artifacts make recurring appearances throughout the series, it is explained in-universe that these artifacts have a will of their own and never stay with a particular wielder for long. In a few cases, to acquire the item, the Daedric Prince has you relieve it from it's previous master (usually lethally).
- In Darths & Droids, referencing the One Ring that "wants to be found", there is the Lost Orb of Phanastacoria, which "wants to be lost". It's only a matter of time before it becomes the Lost Orb of Phanastacoria again.