Worry i can tell doesn't solve problems. But then it almost seem impossible not to worry. Then I wonder why God would have to admonish us to not do something that humanly speaking is impossible. Its is because when we know this is a solution to something we face and that this solution is certain, then there will not be any place for worry. Casting our cares upon him then is what we ought to do always when face with challenges. By doing so we are left with no challenge since all has being cast to him to deal with. But then we must learn to abide in his word and in fellowship with him so that our trust in him is without borders. This will help us not worry after that we have cast our cares upon him.