"When I say 'let's keep in touch', I really mean I wish that you'd grow up..."

Why is it that some people never seem to get over themselves?
I mean this is several ways...
Like when people hold a grudge for months, or even worse, when they never let go of it.
Or when someone can't apologize when they're wrong, whether they even admit to themselves if they're wrong or not.
Like when people break up and they can't just maturely say "hey, we're no good for each other, let's part ways and just be friends like we were to begin with."
Or when someone mentions something they don't like about us and we have to pester them about it, trying to find out details and examples because we are just so sure that they must be wrong, because we want so badly to pretend we're perfect. Even if we all know we're not, we don't like other people pointing it out.
Or how if you do something rash, and then apologize, you still never seem to be able to live it down.
Or how when you tell the truth to someone you care about, sometimes that makes the situation a lot worse than it ever would have been otherwise.
Or like when people choose sides and talk about other people when they're not around, rather than just confronting them and letting them know what the problem is.
Or how people think it's okay to ignore someone when you're upset with them.
I don't really expect any answers. Today I just realized I am so very tired of thinking about these people.