A glad heart makes a cheerful face, but by sorrow of heart the spirit is crushed.
Proverbs 15:13 ESV

Although this seems at first to be a tautology, it is actually contrasting the extent to which emotional states impact the whole person. A "glad heart" comes out in the world in the form of physical and verbal expressions, but a sorrowful heart cuts inwardly, beating down even that which cannot normally be harmed by the physical world.