When I heard this song the first time, I was attracted by the melody.

Then, I listened the lyrics. Smile? For protecting yourself?

What do I smile for? Because someone told me a joke? Because I want to give someone a friendly impression? Or becuase I need to be polite? Or, I'm really happy, so I want to smile?

So, are you really happy? Or as the song sings You're not really happy ?

Hope you be a happy person, then smile, from the inside.