In Avengers: Age of Ultron, almost everyone took a shot at lifting Mjolnir, but only one came close: Steve Rogers. While Steve was unworthy to lift it, he moved it enough to cause Thor to drop his stupid grin for a second. Steve has died to save people (Captain America: The First Avenger), but his loyalties ultimately lie with individuals (as seen in Captain America: Civil War): he is "unworthy" because he puts his friends above others. Vision was able to lift Mjolnir because he was intended to save innocents (by design), and hadn't had the opportunity to do much thinking about who he was in relation to that programming. Would Vision still be worthy after Civil War? I'm thinking it's less clear:
By comparison: Thor destroys the Bifrost to save the frost giants of Jotunheim, them spends two years fighting for peace across the nine realms before getting back to Earth to see Jane Foster (Thor: the Dark World - even then, only because she disappeared from Heimdal's sight). In the meantime, he visited Earth to collect Loki and to fight the chittauri invasion (Avengers), but left without seeing Jane. Crappy boyfriend, but worthy to wield Mjolnir.Captain America: Civil War wrote:Stark: "How did this happen?"
Vision: "I became distracted."
Stark: "I didn't think that was possible."
Otherwise, we have magic items (relics) introduced in Doctor Strange that are treated as intelligent or discerning at least, so Mordo and the Ancient One are surprised to see the Cloak of Levitation on Strange ("It came to you?" "It's a fickle thing.") If Strange is already aware of powerful magic items having this kind of... attunement prerequisite(?), he might approach Mjolnir with an even better understanding of it than Thor does* (Thor isn't a "wizard", while Odin is. Sort of.)
AlsoMordo wrote:Some magic is too powerful to sustain, so we imbue objects with it, allowing them to take the strain that we cannot.
So it may not even be Odin's enchantment but Mjolnir itself that's making the determination: the keyed condition from Thor (2011) may not be the basic condition of 'worthy'.You're ready when the relic decides you're ready.
(Many of the online search results I ran across were focused only on the comics version/continuity. I'd like to concentrate on the MCU version of characters and events/history.)
*Doctor Strange may be in the best position (short of Odin) to actually define the terms of the enchantment for the audience. Also, with Mjolnir's destruction in Thor: Ragnarok, Odin or Strange will have to put it back together, right? Suddenly the manner in which relics are described in Doctor Strange make more sense for the way Mjolnir can function: perhaps the immobility and extra hard-hitting-ness come from "borrowing" inertia or force or gravity from "the heart of a dying star", rather than being one of the more technological explanations fandom has put out there.