SPOILER ALERT: do not read if you ever plan to watch Copenhagen, Drive, or Like Crazy and want to be as disappointed and angry as I was with their sub-par endings (oops, I think that was a spoiler in itself). Nonetheless, proceed reading with caution.
I'm not even going to pretend to be the type of artistic person who can appreciate when a movie ends in the opposite direction of how you thought it would (i.e., unhappy endings). It's kind of like that moment when your parents finally admit to you that Santa isn't real, and they've been consistently lying to your face this whole time. You don't want to be rational. You kinda just want to get unreasonably angry at everyone that's told you otherwise over the years, and wallow in the pain of believing wholeheartedly in something superficial.
I'm irrational in the sense that I develop somewhat of a sense of anger and betrayal. All of a sudden, you're emotionally invested in a plot line, and you watch it crash and burn in the last scene - whether it's Ryan Gosling's character (who remains unnamed throughout the film) at the end of Drive neglecting to knock on Irene's door, or the depressing unhappiness/exhaustion lingering in the shower between Jacob and Anna in Like Crazy, or the fact that Effy and William from Copenhagen never even hooked up/saw each other again.
We're used to the typical girl-meets-guy-then-continues-relationship-happily social dynamic. Even we, the cynical public, are satisfied when endings don't exactly carry out in the way we imagined (ex: Ted/Robyn from How I Met Your Mother... I was always cheering for Barney). Yet, we're entertained with the idea that these characters still end up together, even if it is a different place on the spectrum of friends/lovers/anything in between.
But if an ending is defined as "an end or final part of something, especially a period of time," then don't these kind of movies sort of... do it right? It's the ending of a movie, yes, but in these types of raw, unfiltered, unabridged-versions-of-the-truth films, it's also the end of a relationship. You saw it blossom, witnessed its moments of magic, and in the end, had to come to terms with the fact that this relationship ceases to exist anywhere beyond the end credits - nothing more than that.
A rational response is to be angry and beg the question, why? And you do, when you leave the theater in stunned, angry haste; when you have to watch a happy episode of Friends right after a harsh movie ending in order to raise your endorphin level back to normal. Why make a film that displays such an intimate affair between two people, filled with trials and tribulations, only to have it end in more bitter than sweet circumstances?
I think, maybe, unhappy endings contest more candidly to real life relationships. You put up with all the crap and bullshit that comes with relationships, believing in that "happily ever after" (whether that means marriage, a successful long-distance relationship, or even a date to prom), only to discover that things do end, no matter how much either of you fight to prove otherwise.
There's still value in all of that, though. Maybe as humans we get blind-sided with the possibility of a budding romance in movies, and in our own lives, that we neglect to see how two people can make each other grow and change - even if the end is inevitable. All relationships, on screen and off, are filled with peaks and valleys, highs and lows, good moments and bad. It's unfair to disregard the tidbits of magic between two people just because it came to a natural end.
It's like that scene in The Graduate, when Elaine asks Benjamin if they're going to get married tomorrow, or the day after that, and Benjamin just replies, "I don't know. Maybe we are, and maybe we're not." Maybe that's all we can really ask from any relationship on our own lives, to ride out the possibility of a future and to kind of just appreciate it for what it was and move on when it's all over.