Ephemera put on smile

I'm not in the sky
I'm not on solid ground
I cannot lie
But I know how to pretend
I'm not in the mood
Don't feel like jumping for joy
Though I should
Be happier than medium okay
When my put-on-smile is gone
I am weak
When you think I am strong
I am no better
Than the weakest one
Not made of silver
Not made of gold
I have not seen what
But I have been told