The natural nature can't fathom that. It is hard to understand that joy is not dependent on your circumstances. Remember, it's the joy that feels so good, not what's around you. So if it's the joy you want – go to the only one who is true joy. Let the Lord dwell in you and the joy will come with Him. I don't mean “Cheshire cat grinning” happy. I mean true joy, the filling to the brim fullness that only God's presence can bring...and that doesn't depend on your circumstances. So, just because things get tough, doesn't mean that your joy has to disappear!
Instead, when difficulties come, concentrate on staying aware of God's presence in you and not the problems around you. If you make the problem and its solution secondary to staying close to God, you get both the joy and the solution! Endure the fire – it's producing pure gold!