It's a verse often used in certain quarters, under the rubric of encouragement, to bludgeon the hurting for a failure to demonstrate happiness in pain. No thought given to the harm this misapplication does or what it implies, namely that God is not to be found in the pit. Not only is this scriptural illiteracy ("De profundis", anyone?), but it seems to me tantamount to a denial of the incarnation.
No thought is given either to what "the joy of the Lord" might be beyond grinning through grief. But we have here a possessive--"the joy of the Lord"--therefore, it's God's joy, not the believer's joy in him, that is the source of strength. What is God's joy? Perhaps it is the ceaseless adoration of each person of the Trinity by the others, the joy that Rowan Williams explores in relation to Rublev's icon of the hospitality of Abraham, also known as the Old Testament Trinity. We glimpse it at Jesus's baptism and again at the transfiguration in the voice of the Father coming out of the cloud. God's joy breaking through into a broken and fallen world, a world of sorrow and grief. Joy in the Man of Sorrows. That joy is in the background of Jesus howl from the Cross, "Eloi, Eloi, lama sabachthani?", perhaps (depending on how you view it) the only time when this ceaseless adoration was interrupted.
This is not, is never, a joy that ignores, denies or glosses over suffering. It is a joy that enters pain and grief, comes alongside it and redeems it because the suffering of the Man of Sorrows, the Son of Joy, is eternally part of the life of the Trinity. ("Those wounds, yet visible above ... .") Holding joy in one hand and and grief in the other, this is the life the Body of Christ is meant to model to its members and to the rest of the world. Which is why lament and worship should always be found under the one spire.