Despite the obvious exception of Avengers: Infinity War and Endgame, most MCU movies tend to come to pretty happy endings. The heroes win, humanity is saved (if a little bloodied) and everyone goes for a kebab while they wait for the next threat to all known life in the galaxy. Sun rise, sun set.
Obviously there are obvious exceptions where there's something pretty ominous immediately sign-posted, like Thanos smiling at the end of The Avengers or Loki revealing he's usurped Odin in Thor: The Dark World, but you're not exactly supposed to miss those messages. They're stingers designed to keep you invested in the drama of the expanded universe.
It's more intriguing to think of the more insidious implications of how MCU movies end, particularly when characters seem to have enjoyed a happy one. Because when it comes to expanded universes, you're not allowed to ignore a single brush stroke, which would have to include the disturbing implications the film-makers would probably prefer you missed...
12. There Is A Giant Monster Running Loose In London - Thor: The Dark World
Post-credits sequences in MCU movies have a lot to answer for sometimes and they're particularly problematic when a film-maker does something for a throw-away joke that leaves a gaping logic hole in the rest of the MCU. It's like the idea of the Infinity Gauntlet being introduced as an Easter Egg in Thor and then Taika Waititi having to address it later to plug a hole (more of which later), except sometimes there's no plug.
That is very much the case with the stinger on Thor: The Dark World that establishes that the Frost Beast that chases Thor and Malekith in Jotunheim when they teleport to the icy realm and then followed them back to Midgard is still around. It's played as a gag, as if to say "look how funny this is, a big monster everyone's forgotten LOL!"
And then you realise that that's exactly what it is. It's a giant, murderous, feral monster running amok on London where nobody has any experience of such things and where there are millions of walking snacks for it. Imagine surviving the end of the world only to then be eaten by a big spiky hell hound. It has to have happened to at least a few people.
11. Hawkeye's Life Is Ruined - Avengers: Endgame
Hawkeye's life will never be the bed of roses it once was. And no, not because he has to live the rest of his life with a psychopath who eats mayonnaise on her hotdogs...
Think about it: when he and Nat are standing on the cliffs of Vormir, weighing up which of them deserves to die, Clint says that Nat "knows what's [he's] done" in the five years since his hotdog ruining family were decimated as part of Thanos' snap. He's alluding to the fact that he's gleefully watched the life eking out of hundreds - possibly thousands - of crime lords and their underlings, enacting his own one-man campaign of bloody vengeance. It was all in the name of moral goodness, but it's problematic to say the least.
And worst of all, how on Earth is Clint ever going to get another wink of sleep knowing that's what he did? Every time he killed, he got closer to darkness. Every time he killed, it got easier and cost more to his heart. He even seems to please with Nat to let him die, EVEN THOUGH HE KNOWS his family will return if the Avengers "Time Heist" is successful. Because he can't live with himself.
Yet, here he is, at the end of Endgame, forced to do exactly that.