I finally figured out why girls will stay with guys that treat them like crap, and vise versa if it applies. You see it's not just that they're blind to the situation, well maybe it's a little of that, but it's mostly about insults. You see when you point it out to someone that their partner is bad for them they immediately will tell you that you're wrong, or that you haven't seen it from their perspective, or even tell you you don't all the qualities that they have, just one excuse or another. True or not, what it really is that by insulting their partner, they feel as if you are insulting them and thus they have to stand up for said partner. So the more this happens, the more they feel they should stay, "because things will get better."
For example, I compliment a person on their shirt. "Oh, that's an awesome shirt you have!", "Oh why thank you." You see I'm not really complimenting the person, I'm complimenting the shirt. They didn't make it or design it, but they still take the compliment. Really, what you are complimenting is their taste in fashion. Same thing if I say I don't like their shirt. I'm not insulting the person but in a way it feels like I am because it was their choice to buy the shirt and wear it. Same thing with people. If insult a girls boyfriend who is mistreating her, and go through the trouble to point out all the reasons why she should leave, then she will stand up for him. Not because I'm wrong, but because subconsciously I'm insulting her. Because she was the one who chose him. That's why she wont leave. Because, in a round about way, I insulted her, and now she believes that she has to prove me, and the rest of the world, wrong by staying with him.
I'm sure part of it is from love. Maybe they were happy at first, and memories of that keep her wanting to keep trying. But people are complicated creatures and what's logical doesn't always coincided with our hidden emotions. I'm sure there are other reasons why a person might convince themselves to stay, but I really think that this is one of the bigger hidden reasons why. Or maybe it's just something we never consider.