You know the ones I'm talking about. The solid, sensible, reliable girls. Maybe they're clever, maybe they're not. Maybe they're pretty in an understated kind of way, and maybe they're not. They are the girls that everyone likes, but nobody wants to be like.
They make great friends. They won't let you down, ever; not even if you neglect them -- and you probably will. They'll be there for you, to give you what you need, when you need it. Help with your homework, a shoulder to cry on, distraction for your date's dorky friend, they'll provide it.
They do the responsible things. They are head girl, they edit the school paper, organise the prom.
They are the girls that the boys want to marry. Eventually, when they've had enough fun with the bad girls. They are the girls that the boys' mothers want them to marry too.
It isn't that they are self-sacrificing, not really. They are just nice. They like to be helpful, enjoy making other people feel good.
What happens to them?
Nice girls become nice women. If they are straight, most of them marry, and if they can, have a kid or two. They turn up on committees, they get involved.
They take responsible jobs (the clever ones get good degrees first of course), and they do them well. They keep doing them well even when they are passed up for promotion, because they are too valuable where they are. They might run a small company, but you won't find them as CEO in a large corporate.
Only one in millions will ever really "make it", and when they do it'll be in a self-effacing, probably solitary field -- as an author maybe.
And they will live quiet lives, more or less content, and more or less bitter, being there for their friends, for their partners, for their bosses, for their kids. Keeping people and things together.
Without them, things start to fall apart.
What happens to the nice girls? Somewhere, behind the scenes, they end up running the world.