Wall of Text!
'Scool. It is not TL and I did in fact R.
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Easy bit out of the way first: OP specifies physical attractiveness. Imagine a picture of a pretty person. That's who we're talking about.
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Sure I'm making generalizations; I'm doing what those fancy book-learnin people call extrapolating. I'm not going to claim that it's true 100% of the time for 100% of the people, but I don't think it's exactly controversial to say that physically beautiful people are as a whole more likely to be outgoing and confident than the uggos. I mean, c'mon. They're
uggos.
I don't know if anyone even still uses that bit of slang these days.
I would argue that the military is a subset and probably not a representative sample of the human race as a whole. The guys who aren't uber-self assured self-styled
mean mother fuckers on their way into the army are whipped into shape relatively quickly. There may or may not be pretty boys in the armed forces --
James Blunt somewhat famously served in Kosovo and was by reports far more of a badass than anyone who writes shitty pop music for a living has a right to be. Regardless, everyone gets the same training. I mean, that's the point, right? Train a bunch of nameless fierce sonsabitches who will fight and die for (insert country/cause here). You're not going to get results by teaching them all to talk about
feelings.
Granted I know slightly less than Hollywood about what actual military life is like, but this seems like a reasonable assumption.
Anyway, I think you got it backwards. I'm not saying that you have to be good looking to be confident, or ugly to be timid. All I'm saying is that we tend to give more concessions to folks who are more confident, and that beautiful people tend to be more confident. They trend in that direction, if you prefer. It's not universal, but it's something that in my experience at least seems to hold true more often than not.