theories of behavior

Class, on the topic of avoidance, I wanted to bring up the concept of approach goals and avoidance goals.   We know that we're often more motivated when we're running toward something (an approach goal) as opposed to trying to avoid something.   Why do you think this might be the case?    Most goals can be phrased as both an approach goal and an avoidance goal...I might attempt to set an approach goal for a new job, or I could set an avoidance goal to leave my old job.    

What makes the difference here, and how might motivation be impacted?

about 150 words