A happy heart makes the face cheerful,
but heartache crushes the spirit.
(Proverb 15:13)

Our face is often a reflection of what's inside.  It's not beauty-based, it's soul-based.  We can put on a smile, but if that smile doesn't match what we are feeling inside, it comes off as insincere and we really don't fool many people.  I'm pretty guilty of trying to put on a happy face, regardless of what's going on inside my heart.  Sometimes I can fool people, sometimes I can't.  I can never fool God.