Human beings are social creatures. We build our identities based on our relationships with the people around us. To the extent that our biology dictates anything, it dictates that we will care about what other people think.
Shunning and shaming have been used to enforce social and legal standards throughout human history and across cultural lines. Solitary confinement of prisoners has been rightly called torture, and permanent brain damage has been documented as a result of it.
It will come as news to no one that men and women get different social messages when it comes to sex. Men are told to have it, or else. Women are told not to have it, or else.
That "or else" is not a trivial thing. No one will beat you, imprison you, murder you, or otherwise do physical violence to you if you don't conform to these ideals (usually), but that doesn't translate into the ability to break from your assigned role without consequences. And as I noted, the consequences of social ostracism are very real for social creatures like human beings.
The more observant of you will have noted that the gendered expectations above are contradictory. Men are supposed to have sex with women, but women aren't supposed to have sex with men. It's impossible for both these outcomes to be happening simultaneously. No matter which way it comes down, someone will end up hurt and shunned.
In that context, I think I have an explanation for that old chestnut, "nice guys finish last" as it applies to dating.
Women want to have sex, but are told repeatedly that doing so will have negative social consequences. The term slut shaming has been used in feminist circles to describe this very real and not at all unreasonable concern women have. By consenting to sex, a woman opens herself up to shaming and ostracism.
Pickup artists figured this out a long time ago, and they've picked up on how women manage to have sex while attempting to shield themselves from the worst consequences of slut shaming. They never unambiguously consent to sex. Pickup artists council giving a woman plausible deniability, so that she'll be able to say "it just happened" when all is said and done, so she won't have to deal with the social consequences, many of them internalized, that come when she chooses to consent to sex.
Now, that's a problem for nice guys. Nice guys care about sexual consent. They care whether the other person is uncomfortable, and will always seek explicit, unambiguous consent at every stage of a relationship. And as a result, they're unintentionally denying women the ability to pretend that "it just happened."
Bad boys, of course, provide all the plausible deniability a woman could ask for. They demonstrate at every stage of the relationship that they do not respect other people's boundaries, so a woman with one never has to consent to anything.
It's a tidy arrangement, but for one simple fact. Sex without consent is rape, and women employing this strategy are never having explicitly consensual sex, by design. I can think of no clearer an example of rape culture than the fact that our standard relationship model involves women putting up boundaries explicitly so that men will push through them.
Meanwhile, nice guys are being told they're defective.
Remember those messages men get that tell them just as strongly and just as often that they are supposed to be having sex? So they start asking questions about why they are failing to get sex, often aggressively, because they are being shunned and shamed. Men aren't inherently sexually aggressive beasts any more than women are asexual ice queens. We're both trying to conform to social expectations because there are very real consequences to us when we don't.
So what answers do nice guys get? They get told about confidence, that jerks are confident, so they're more attractive than a nice guy who's feeling like a failure. But that's wrong. It isn't a lie. It's just wrong.
You look at a nice guy and try to see what's wrong with him, and you don't see any flaws. He's decent, caring, sensitive, and has his shit together. But you have to tell him something because what he's doing obviously isn't working, and you are a decent person and don't want to see him continue to be hurt by his romantic failures.
You look at what possible positive traits he could be lacking, and the only thing you can find is that maybe he's lacking in confidence. So you tell him to work on himself, try to be happy alone so that confidence can build up and then he'll naturally be attractive because that was the only thing you could perceive that might be even slightly wrong with him.
But that perception that nice guys lack confidence is rooted in two errors. First is that lack of confidence is an effect, not a cause. He lacks confidence because he's being subjected to shaming and ostracism for failing to conform to his gender role. He's experiencing exactly the same social pressure that you try to avoid when you worry over being called a slut. That's what is eating away at his self esteem, and the only way out of that trap is to either conform to his gender role and succeed at having sex, or to recognize the gender role for what it is and reject it outright.
The second error is mistaking a willingness to push through boundaries as "confidence". Being unwilling to push past boundaries and make someone else uncomfortable isn't lack of confidence. That's respecting the other person as a human being, and accepting the words and signals telling you that your advances aren't wanted.
So, with all that mess, what is a nice guy to do?
First off, you're a decent human being. Don't change that fact. Yes, pushing past women's boundaries in order to let them avoid slut shaming is what they want, but letting them play that game only makes it harder for them to come to own their sexual choices and desires.
Second, you're a decent human being. Decent human beings don't slut shame. When a woman agrees to have sex and owns that decision, never make her feel like she did something wrong. When someone else makes a woman feel like she did something wrong by agreeing to sex, that person is part of the problem, and needs to be called out not just because he's being an asshole and hurting that woman, but also because he's perpetuating the system that makes women think they need to be able to say "it just happened".
Third, and this is going to be the hardest part for decent human beings. Don't let a woman say "it just happened." When a woman uses those words, I recommend (and have used) the following script:
W: It just happened.
M: Were you raped?
M: Then it didn't "just happen." You made a choice, and there's nothing wrong with that.
I realize that this is hard to say, but the truth is, you're doing a woman no favors by letting her hold on to her deniability with you. Because whenever you're told "it just happened," it's because she's afraid that if she told you she chose to have sex, you would slut shame her. This script tells her that you are not going to slut shame her, and that she doesn't need to pretend.
This won't get you sex.
That isn't what the goal is. You're a decent human being. You will feel like shit if you start pushing past boundaries and having sex without explicit consent. If you were willing to do that, you wouldn't be a nice guy having this problem in the first place.
This is about confronting the underlying problem that leads to all those boundaries being put up in the first place. The goal is to get to the point where women have the confidence to say they want sex when they do.
You want to have sex with women who want to have sex with you and aren't afraid to say so. Pushing past boundaries, no matter why they were put up won't get you that. Breaking down the cultural expectations that are telling women they're wrong to want sex with you might.