To paraphrase a quote often mistakenly attributed to Albert Einstein: people who repeat the same mistake over and over and expect it to turn out differently are some dumb motherfuckers.1
When it comes to dating there are a handful of ways people do this:
a) Dating someone who already dumped you once even though they've already shown they're not worthy of your time--and expecting things to go better the second time around 2
b) Dating someone who already hurt you once, forcing you to leave them...and expecting that they won't hurt you again at some point 3
c) Dating someone who is exactly like the people who've already hurt you and dumped you even though it seems likely there was incompatibility issue and it may be in your best interest to change up the formula
d) Not altering the way in which you find people to date. 4
e) Not altering the criteria you use when deciding with whom you should get involved.
The last one seems to be the most tricky. The others typically seem to take care of their self after a while. Eventually dating your ex will burn you again. If you date enough assholes, you usually reach a point where you're sick of it and wise up.5 If you keep dating in your social circle you'll eventually run out of friends, coworkers, neighbors, classmates, and fellow churchgoers. And everyone wears out of meeting people up in the club.
With those first four you can all rationalize it as being problems with the other people. Of course it takes two people making poor decisions to start a doomed relationship. But you don't have to admit that in cases A through D. But with case E? That requires a bit of hardcore self-analysis. Some real looking in the mirror and facing yourself down shit. And not many people are willing to do that.
In the movie Up in the Air it's played for comedy. Young Anna Kendrick lists off all the requirement for her dream guy, right down to appearance, the way he'll dress, and how he feels about pets. And Vera Farmiga replies that all of those expectations will be gone by 30.
And that can seem like settling. But that's total bullshit. As you get older it's not that you lower your standards. It's that you learn how artificial some of them were in the first place. And you start to place more emphasis on the shit that really matters--compatibility and personality. As opposed to aesthetics or smooth talking. Your standards at 22 are not more rigid--they're just stupid. And often confused by your out-of-control hormones. There's a reason that most people who get married in their early 20s do not make it last these days.6
When I was 22 I was fucking romantic purist. I don't mean that I wanted romance to be like a romantic comedy with Lloyd Dobbler wooing some chick with a bunch of wit and rambling. Or that I wanted tons of snappy dialog akin to every single movie that involved Kate Hepburn or Cary Grant in their youthful prime.
I mean I had visions of undying, candle-burning-at-both-ends, Heathcliff & Catherine, meant-to-be love. I think I believed in that up through my mid-20s. To the point that I wouldn't even pursue something that I knew was a dead end. Not even just to get laid. And it goes without saying that in my mind the "meant to be" woman of my dreams would have to be a stone cold fox who was also a sex goddess who wore short dresses. And, despite what I said earlier, she'd of course be some blend of Kate Hepburn and Audrey Hepburn. Kind of smartass beautiful princess.
If there was a god, I would have gotten by heart broken a few times at a young age and quickly wised up.7 Alas, this did not happen. And it took my most of my mid-20s to realize that maybe I was doing things wrong and there's more to making a relationship work than feisty women in short skirts. Though, really, those things are still pretty nice.
1) "The definition of insanity is doing the same thing over and over and expecting different results." - Rita Mae Brown, though often credited to Einstein, Franklin, or Twain
2) I realize there are people who get back together after a long time off and it's better the second time. This is not true love. This is settling. For one or for both parties. Usually the latter. As in "I'd rather be miserable and predictable than miserable and facing the unknown." Note that the re-acquaintance almost always takes place after they've had problems meeting someone new.
3) Cheaters might not always be cheaters, but people who don't give a shit about the consequences of their actions will almost always continue to rationalize bad behavior
4) If you keep fucking your friends, maybe it's time you re-think that move. Likewise with your co-workers. If you keep going home with skanks from the bar who really like your ride then you might want to change that up, too.
5) Hopefully it's before you have kids. Because it's really fucked up if you have a kid and you're still bringing assholes home. Though I see it. Plenty.
6) Olden days were different. People were more mature at 18. Plus, half the time you married for convenience other than true love. Often to the first person you met. And you made that shit work like an arranged marriage because that's what you were supposed to do. Also, women were supposed to not work and men were allowed to drink at work and fuck around. Or so I've learned from 4 seasons of "Mad Men."
7) OK, actually, if there was a god then this version of my own manic pixie dream girl would have totally existed and she would have found me living in SC and seduced and married me and we would have lived happily ever after and been filthy fucking rich