Often when I walk down the street, I say hi as someone walks by. And I find, others don’t always say hi! Maybe I wasn’t clear or loud? Maybe I have something in my teeth? Maybe my smile is too creepy? No.
OR… Maybe they’re just rude? Thinking something, busy worrying? Think I want something from them? Who knows! I’m not sure why others don’t always say hi back.
That being said, I think it’s a great practice to NOT be reactive. To not get hurt or offended. To not fundamentally change your nature and continue to be friendly and say hi. 
This practice can easily follow in situations in life when others don’t do as we’d like to – keep on keeping on.
This practice can easily follow in situations in life when others don’t do as we’d like to – keep on keeping on.P.s. That being said be socially aware and smart – check yourself! Don’t smile in Compton or something haha but generally I feel it’s a good thing to be positive and friendly. It’s better than the alternative, to be bitter, mean, or checked out or numb.