You worry because you are not prepared to go with the flow of life, you want to control your life. So you worry about things that might happen which you do not want. And if those unwanted things happen what you will do, how your control will be lost, how you will have to get out of your comfort zone, etc. But if you get lose of your notion of control and instead of trying to control the outcomes in life you just go by the flow doing your best at any given situation, you will experience more peace and happiness as there will be less things to worry about.
What will happen or won’t happen won’t get changed on the basis of your thinking, but by thinking them anyway you only ruin your state of mental serenity and peace. Therefore, be wise and do not worry. Trust God for He is just and will take care of your future. You focus on and take care of the present. Had He not assured to not worry about your life as the Heavenly Father knows what you need? Had He not declared that He takes care of the needs of His devotees? Therefore, refuse to submit yourself to worry, be diligent and faithful instead.