(Warning - mild SPOILERS for Avengers: Age of Ultron are to be found below, so proceed with the requisite amount of caution...)
Now, in a movie filled close to bursting with intense action set-pieces and memorable quips, there were still few more awesome moments than a quiet scene of the Avengers hanging around after a big party...and trying to lift Thor's enchanted hammer.
After all, what better way to unwind after months of fighting HYDRA than to attempt to lift a mystical weapon magically bound to 'whosoever shall be worthy' - which, in this case, is very much Thor - in spectacularly unsuccessful fashion:
The most intriguing thing about that scene, though?
The fact that Cap almost manages to lift the hammer...
The thing is, though - for all that the scene is adorable and whatnot, it actually raises a pretty big question:
Why COULDN'T Cap Lift Thor's Hammer?
After all, not only is he clearly worthy enough to lift it a fraction - suggesting that it is indeed possible for someone else to lift Thor's hammer in the Marvel Cinematic Universe - but it wouldn't actually be the first time Cap has lifted the mighty Mjolnir...
In fact, in the comics, it happens all the freaking time...
So much so, in fact, that even Superman and Wonder Woman have managed it (in the periodic DC/Marvel crossovers that the 1990s and 2000s gave us)...
...as has (admittedly while utilizing zero gravity) the distinctly un-worthy Iron Man:
So, if there's comic-book precedent for Cap being able to hold the hammer, as well as confirmation within the movie that he is theoretically able to do so there too, then why couldn't he lift it?
Well, the simple answer, it seems, is that:
Cap Isn't Actually Worthy
Yup - that's right: The most logical explanation for Cap not being able to lift the hammer isn't that he's human and Thor isn't, or that there's anything scientifically fishy going on. After all, as Thor himself said, it's simply a matter of being worthy.
The gigantic elephant in the room, then?
Why ISN'T Cap Worthy?
Well, the best explanation I've seen for that actually comes from Quora-er Ishita Roy, who's pointed out something incredibly important about the nature of 'worthiness' when it comes to Thor's hammer.
Y'see Cap may be an honest, noble and genuinely decent man - and as much of a hero as anyone could ever hope to be - but he still fails on one key point: He is, as Roy puts it, a 'Blood Knight.' Specifically, "he defines himself solely through his ability to fight."
Which, from the hammer's perspective, is a problem, since:
Thor Is Only Worthy Because He Rejected 'War For War's Sake'
After all, it was Thor's love of fighting for fighting's sake, as well as his general lack of compassion, that saw him banished from Asgard in the first place (way back in Thor), and it was his evolution into a more peace-loving figure that allowed him to regain his hammer, and his place in the Norse pantheon.
Cap, on the other hand, literally saw his own worst nightmare in Avengers: Age of Ultron - and it was the war being over:
Now, sure, Cap will almost certainly intellectually wish that there'd be no more wars to fight - but he clearly isn't hoping for that day to be anytime soon.
After all, even his objections to Tony Stark's creation of Ultron seem to ultimately boil down to 'you can't stop war this way,' as opposed to a broader moral argument about authoritarianism and free will.
All of Which Presumably Means that Cap Isn't Worthy...Yet
He is, however, obviously heading in the right direction - which makes sense, seeing as in every other possible way he's about the most inherently heroic person you could ever imagine.
That tentative lift of the hammer, then?
That's an indication that Cap is on the right path - unlike, perhaps, his fellow Avengers, who are tainted with their own pride, or even lack of moral purpose - and that he just needs to go through the same kind of realization that Thor did.
Y'know, the exact kind that he could well be set to go through after being forced to fight his friends in next year's Captain America: Civil War...
Or, in other words? If Thor does indeed (at least temporarily) die in Thor: Ragnarok, as is widely expected, don't be too surprised if Cap - changed by his experience in Civil War - ends up lifting briefly lifting the hammer in Avengers: Infinity War...
Or, y'know, that the whole 'hammer-lifting' sub-plot never gets mentioned again. Either way...
What do you think, though?