It's mostly an AA problem, but I'd like to elaborate. It usually happens like this:

I'm out in the city, a shopping mall, etc., and I see a pretty girl. I look at her, seeking eye contact. She will look at me for a split second and that's it, look away instantly. I find this even more discouraging than approaching from "the dark". When a girl hasn't seen me yet, I feel like I could walk up to her and get her attention. But when she notices me but looks away, it feels like she just doesn't want me to approach at all. Now, of course, you could say that I could wait for girls who maintain eye contact with me, but that would leave me with 0 decent-looking girls.