The word pride has many subtle shades of meaning, Kitty, definitions dictionaries don't always do justice to.
One can certainly feel pride in accomplishment, although that's probably not what most of us mean when we talk about LGBTQ Pride.
We can be proud of accomplishments, like coming out, which we all know can be really really hard. Finding the courage to do that is worth celebrating, and there's nothing wrong with feeling a certain sense of pride in it.
But I think the pride that most of us mean is more basic than that. It's a pride in self, a recognition of health and goodness inside ourselves.
I think this can be hard for cis/straight people to relate to, because they mostly don't grow up having it pounded into them that they aren't quite right, that they aren't quite healthy, that they need to change.
We do, so our innate inner Pride is something we all know deserves celebrating. It's about holding our hands up high and proclaiming our wholeness. But more importantly, it's about knowing deep down that nothing is wrong with us.