Do you fake smile?

You are walking by down the street and there is an eye contact to some stranger. What do you do? Or- you push the door to open and someone walks from opposite direction. What do you do?

Yes - Obviously we smile. But have you noticed anytime the way people smile? You see a BIG smile on their face and suddenly its gone. You know, like a trained robot? You see someone, then you see a smile and then whoosh, its gone.

This is something I have failed to understand. Why do people smile half halfheartedly? Courtesy sake? People are taught in school/home to do that?

What use is a smile if it is followed by a stern face or a frown? Meaningless! What does it take to keep it on for a few seconds more? Till someone to whom it is intended even realizes you smiled?

C'mon people, don't be in a hurry and leave things incomplete. Smile with all your heart; it could brighten someone's day. It could be one of the best things the other person has seen all day. Don't ruin it by making it mechanical.