A person might endure terrible suffering and not be able to express what is in his heart. There is no one to whom he can unburden his heart, so he remains deeply pained and worried. If you come to such a person with a happy face, you can literally give him life. This is a great thing and by no means an empty gesture.
Reb Noson of Breslov; Rebbe Nachman of Breslov. Rebbe Nachman’s Wisdom #43