James 1:2 says to "count it all joy when you encounter various trials."
All of us experience trials but how can we go through them and experience full joy? There is only one answer, trust. We have to trust God that He is in control of our lives. It is when we do this that we are able to count it all joy. Maybe we could phrase it "no worries." When we stop worrying or fretting over our situation and trust God then we can experience His joy. So "be anxious for nothing" or "stop worrying." Trust God that He is in control.