1. Marry the first person you meet whom you could happily be married to. Don't settle; make sure you could happily be married to the person, but don't pass up an acceptable partner.
2. Stop worrying about whether you could have met someone better.
Satisficers are happier than maximizers. Don't be a maximizer.
"Marry the first person you meet whom you could happily be married to"
Which implies that for each person, either you could be happily married to them or you could not be happily married to them. My point is that there are probably many people who you could marry and increase your happiness, but that doesn't necessarily mean you should marry the first one you encounter, because of the significant opportunity cost.
Let's look at it, though. For the first 15-20 years (subject to debate) you don't know anything about this problem. You don't know who you are, everyone's changing fast, you're blinded by sexual desire, etc. For the last 30 years, your reproductive viability is reduced for men and zero for women. This puts the "choosing window" at, say, 20 to 50. That would mean that one doesn't settle down until 32 at the absolute earliest, and that most people would do so in their 40s (and have only a few years to bear children). Most people don't want to wait that long to settle down, and for good reasons.
One major one is that the pool of available singles declines in quality as you get older. The Secretary Problem assumes a uniform distribution of quality over time. It's not true (and, in fact, insulting) to say that "all the good ones are taken", but I definitely noticed a change in the average quality of dates from 20 to 26 (when I met my wife and left the dating game). You still can find great people at any age, but the distribution evolves. Because people improve with age (fuck VCs and how they think about that) there's some push at the high end, but that's not offset by the disproportionate rate at which either (a) "the good ones" are taken, or (b) the messed-up people become better at hiding themselves, which is my preferred theory.
(I have no idea whether that decline of available mate quality continues after 26, or if it levels off or even reverses. I know some high-quality people who are single at 40, but have no concept of the aggregate dating scene at that age.)
Empirically, people don't "hold out" during 1/e of their window because, unlike with the Secretary Problem, the payoff in choosing the 2nd or 3rd-best theoretical match is quite high (maybe 0.8 to 0.99) compared to the payoff (0.0 by definition) of never meeting someone as good as the best during your hold-out period.
The 2nd or 3rd-best theoretical match could also have a negative payoff (divorces you, takes half your money + child support + alimony). You can lose a lot more marrying the wrong person than never marrying at all.
It did seem, as a man, that women with good personalities improved with age, but that women with average or bad personalities became worse. Age seems to spread people out, in that way, but the well-adjusted people being selected out tended to push down the mode. There were a lot of women I dated in their late 20s who had way too many psychological cigarette burns from Biffs and Jedds ("two D's because..."). Partners of low moral character definitely do lasting damage-- that's obvious in all genders-- and women have more opportunity to get fucked up (and fucked literally) than men in college and their early 20s.
That said, "all the good ones are taken" is probably more panic than reality. I remember in college, people used to descend on the freshman girls "before they get snapped up". It's a fucked-up way to think and maybe it actually has the opposite effect of taking bad people out of the market, because only a fucked-up person would think that for a college senior to stalk September-frosh ("froshing", it was called) is OK.
The problem isn't physically abusive partners alone. There's more to it than that. If dating a jerk or a crazy person or even a physically abusive person made someone "permanently damaged" there'd be almost no one left.
The main issue that is gendered is that women have more opportunities, when they're young, to involve themselves with really terrible people and for things to go seriously wrong. We're all bad judges of character when we're really young. The typical 15-year-old boy isn't any morally better than a 15-year-old girl, and would probably make choices that would destroy him if given the chance... but typical 15-year-old boys are considered unattractive (even to girls of the same age) and don't get those opportunities. I was a fucking idiot at that age, but no one wanted to be a fucking idiot with me. For women... it's a different story. The opportunities to make really bad choices and ruin yourself, if you're a young woman, are quite available.
I don't think it's even sex itself that does the damage. I used to think that, but I think casual social contact is what erodes the person's values. Being around bad people makes a person bad. What makes college casual sex evil isn't the sex itself (the sex is vanilla) but the acquisitive, manipulative, and dishonest culture around it. I have no problem with swingers or people in open relationships or above-board promiscuous adults, because there's nothing gross or wrong about sex itself. But the culture around college casual sex (the alcohol abuse, the focus on man as conquerer and woman as defeated, the "gray rape" that isn't "gray" at all, the fights, the "pickup artist" nonsense, and the reward of bad behavior in both sexes) is pretty disgusting.
Is that a rhetorical question or do you actually want to know the answer? If you actually want to know the answer, the best explanation I have read is here: http://therawness.com/why-its-worse-for-women-to-sleep-aroun...
The traditional solution to this problem is that the father and/or brother would protect the young woman and maim or kill the louts who would try manipulate and take advantage of her. Colleges also had the power of "In loco parentis" to prevent parties that were full of alcohol abuse and casual sex. All such powers were stripped by law in the late 60's and 70's with the results you see now. So if you want to see this problem fixed you would need either to return to patriarchy, or invent some novel way of guiding the young down the right path.
How To Marry The Right Girl: A Mathematical Solution
1) n = number of people you could date in your lifetime
2) Date n/e people without stopping.
3) After dating n/e people, marry the first person who is better than everyone you've dated previously.
This method selects the best candidate about 37% of the time, which sounds bad but is superior to other systematic methods.
Sources:
https://en.wikipedia.org/wiki/Optimal_stopping
https://en.wikipedia.org/wiki/Secretary_problem