Who regulated my smile

I was given an unexpected bright smile today, feeling like a gift! :)

I realize then, that my smile is no more mine to give out freely. It is a signal, rather functional, and give out only on specific occasions. I smile "professionally" in job interviews, to give a good impression; smile "like a flower" when asking for a favor, to show sincerity; smile to lovers, families and friends... When do you smile to a stranger or ...to a tree, a flower, nothing but only to smile? Smiling girls are the most beautiful, yet I do not naturally do that so often anymore. :(