I'm super late to your party, but here's my 1¢ (my opinions aren't even worth 2¢). Feel free to dismiss and downvote my ramblings.

I was overweight for a long time and I always felt like an ugly kid. Also, being a minority growing up in white neighborhoods I always got the impression that white girls aren't into my ethnicity (Pacific Islander). My weight yoyo'd around for a while, but I eventually lost most of it.

Regardless, I NEVER felt attractive to women and would ALWAYS attribute their attention to some other factor, and simply couldn't believe any of them were attracted to me. It's so uncommon for guys to be told they're attractive. Unless guys actively take steps to change their mentality, they will generally continue thinking the same way they grew up.

As egotistical as it seems, I tried to fix my mindset by writing a list of some odd interactions I'd had with women over the years. I'd finally learned what flirty body language looks like, and realized with hindsight that many of them were actually flirting with me.

I missed super obvious cues like one girl actually felt up my arms at the gym (I'm not buff at all). There was one time these two girls were actually taking creep shots of me with their cell phones (only now do I realize how obvious they were), my girlfriend's friend playfully grabbing my ass, or being told straight up by a waitress, "My co-worker Sunny over there thinks you're cute."

Because of a combination of low self-esteem, no social skills, and fear, I believed I was misreading their signals and my brain came up with many reasons why they wouldn't be into me.

E.g.: "They're just messing around, they don't mean it." Or, "Why's she keep looking me up and down? Do I have a stain somewhere?" And even this gem: "That chick back there keeps staring at me, did I do something wrong? I fucked up something didn't I? Shit!"

So yeah, you could say we're pretty clueless, but it's not entirely because we're stupid (although some of us actually are).

Women are taught from a young age to watch out for certain signs from men and to be on their guard all the time (or so I've been led to believe). Based on my limited experience, I'm going to assume most guys don't get these talks.

My completely uneducated opinion is that as feminist ideals become more ingrained, women will begin to take the initiative more, and older men like myself will begin teaching their own boys what a woman's advances look like. Thus the next generation of guys will (hopefully) be equally aware of social cues as women are and (just maybe) we can have a slightly more egalitarian society.

Apologies for ranting. Bring on the downvotes!

TLDR: Low self-esteem fucks with your head so you miss out on opportunities you didn't realize were there.