Smile even though your freaked out

I always heard the phrase, "smile even though your heart is breaking."
If your heart is breaking, why smile? it seems pretty dumb to me.
if my heart is breaking, i like to eat broccoli and pretend its actually someones head, and that i am biting their head off.
Basically, i never got the whole "smile if your heart is breaking" thing.
until i saw this picture:

It totally freaked me out!!!
then i got it,
if your upset, then you should smile to freak people out and ruin their day, because it will make you feel better.

Do you ever freak people out?
What do you do when your heart is breaking?