The quest for good qualities

Why is it that some people fail to find the good qualities in other people? Isn't there at least a little good in everyone? Or is that truly a naive thought? I was chatting with a friend not too long ago, and he told me how much he didn't like another one of my friends. I said it was strange, that I've never seen them like that before, and it was as though we were looking at two different people. I said it must depend on how you look at it. But he replied, "how could I see anything different if that's all they ever show me?" Pondering on this question, I thought, "Are you sure that's all they ever show you? Or are you only paying attention to that part of them?"
Someone else told me that the reason why people fail to find the good qualities in others is because they refuse to admit to the lack of good qualities in themselves. But to me, they don't lack good qualities, they may just not be aware that they have them. There are people out there who look at other people, and point out what's good and what's bad about them, then they look at themselves and think "Oh, I'm not special at all." When in reality they are amazing people. Is it truly because they refuse to admit to what they think is their lack of good qualities, or is it because they see qualities in other people that they would like to have in themselves?
People are like a prism. They have different sides, and the way the light bounces, or the way you see it, gives you an impression on how it's like. True, it's always different to every person. There's always different sides to a spectrum. There may even be some aspects of it that you may not like. The important thing is, you see the beauty of the prism. You capture more of what you like or enjoy about it, instead of what you dislike about it.