Telling someone "don't worry" is like telling someone to be "perfect". It isn't helpful advice. However, when God talks about perfection, he doesn't refer to flawlessness. He refers to the process of pursuing completeness. The same is true about worry. God knows we will worry because He knows that we are stubborn and selfish and we refuse to trust Him and that causes a ton of worry. However, God desires that we don't "wallow" in our worry. Worry is simply an indication that something matters to us and when things matter, we should give those things to God and ask for his help.
Lord, help me to worry less because I trust more but when I fail to worry less, help me to see it as an indication to pray more.