It is cruel to say to people who are in sorrow, “Smile and be happy." People simply cannot be happy all the time. There is no way that people can paste a smile on their face and go around with a saccharine grin all the time. You are not expected to.
The Bible says of the Lord Jesus: "He is despised and rejected of men; a man of sorrows, and acquainted with grief: and we hid as it were our faces from Him; He was despised, and we esteemed Him not" (Isaiah 53:3).
And yet the Bible spoke of the joy of the Lord. Psalm 45:7 says, "Thou lovest righteousness, and hatest wickedness: therefore God, thy God, hath anointed Thee with the oil of gladness above Thy fellows."
It may be mockery for us to sing “I’m downright happy all the time." It would probably be a downright lie. You see, this is a life of tragedy, sorrow, heartache, and pain. Yet in sorrow and in heartache and difficulty, you can have joy. Happiness is an outside job; joy is an inside job.
Joy comes from the Word of God. John 15:11-12 says, “These things have I spoken unto you, that my joy might remain in you, and that your joy might be full. This is My commandment, That ye love one another, as I have loved you.”