Fear is debilitating when we think we can't handle the outcome of whatever. As I explain (often) to my husband, the difference between worry and concern is whether or not you have a contingency plan. Concern is warranted by justifiable fears, and leads to your developing a plan of action to help you deal with whatever it is, should it happen. It helps you enjoy your present. Worry is when you allow yourself to drain your current moment of happiness because you fear that something bad will happen in the future.