Anxiety serves a

useful purpose, so long as it doesn't spin out of control. Worrying is a rehearsal for danger; the act of fretting focuses the mind on a problem so it can search efficiently for solutions. The danger comes when worrying blocks thinking, becoming an end in itself or a path to resignation instead of perseverance. Overworrying about failing increases the likelihood of failure

But why are some people better able to "snap out of it" and get on with the task at hand? Again, given sufficient self-awareness, people develop coping mechanisms. Sadness and discouragement, for instance, are "low arousal" states, and the dispirited salesman who goes out for a run is triggering a high arousal state that is incompatible with staying blue. Relaxation works better for high-energy moods like anger or anxiety. Either way, the idea is to shift to a state of arousal that breaks the destructive cycle of the dominant mood.