I think I realize that most strangers aren't going to start conversations with me unless they want something or need something. So even if I get random stares for a brief second, they go back to whatever they're doing with their lives.
I also noticed that when people say "hey" I always feel very nervous until I see who it is. Sometimes I'm worried that it might be some girl I used to date or someone from high school who wasn't on good terms with me (or I wasn't on good terms with her) and I never know what we still think of each other.