“Patience is Never Easy”
 
Hand drawn
 

 
So during the “You’ll Play Your Part” song scene, one of Luna’s lyrics is “Patience is never Easy / I understand wanting more / I know how hard it is to wait / to spread out your wings and soar”.
 
I saw pain in her when she sung that. I imagine that that was very painful to face. She knew what Twilight was going through. Luna had waited so long that she rebelled and was banished to the moon, to wait another thousand years to get the love and recognition she deserved.  
I imagine that seeing Twilight have the same worries that drove Luna to rebellion was painful for Luna. I imagine that Luna, when singing these lines, was flashing back to the times she felt ignored and without purpose, and those 1000 years of loneliness she endured on the moon. She had literally waited ages to realize her purpose and importance. So I think this part of the song was very painful for her.